UNIVERSITY  OF  CALIFORNIA 
AT  LOS  ANGELES 


5  ( 


I 


WORKS  OF 

PROFESSOR  F.  P.  SPALDING 

rrm.isHKn    r.v 

JOHN  WILEY  &  SONS 


A  Text=Book  on  Roads  and  Pavements. 

The  aim  of  this  work  is  to  give  a  brief  dis- 
cussion, from  an  engineering  standpoint,  of  the 
principles  involved  in  highway  work,  and  to 
outline  the  more  important  systems  of  construc- 
tion, with  a  view  to  forming  a  text  which  may 
serve  as  a  basis  for  a  systematic  study  of  the 
subject.  I2mo,  cloth,  $2.00. 

Hydraulic  Cement — Its  Properties,  Test- 
ing, and  Use. 

This  work  embodies  the  results  of  a  careful 
study  of  the  nature  and  properties  of  hydraulic 
cement,  and  the  various  methods  which  have 
been  proposed,  or  are  in  use,  for  testing  cement. 
I2mo,  cloth,  $2.00. 


HYDRAULIC    CEMENT. 

775  PROPERTIES,  TESTING, 
AND  USE. 


0.  w. 

VOL  Ho. 


FREDERICK   P.   SPALDING, 

Assistant  Professor  of  Civil  Engineering  at  Cornell  University 
Member  c/  the  American  Society  of  Civil  Engineer*. 


FIRST   EDITION. 
FIRST    THOUSAND. 


NEW  YORK: 

JOHN     WILEY    &    SONS. 

LONDON:   CHAPMAN   &   HALL    LIMITED 

1898. 


Copyright,  1897, 

BV 
F.  P.  SPALDING. 


TT 
37  1 

S7U 

PREFACE. 


THE  following  pages  contain  the  results  of  a  care- 
ful study  of  the  nature  and  properties  of  hydraulic 
cement,  and  the  various  methods  which  have  been  pro- 
posed, or  are  in  use,  for  testing  cement. 

The  subject  is  not  so  simple  as  it  might  seem  to  the 
casual  observer,  but  abounds  in  contradictions  in  the 
results  of  experiments  and  conflicts  of  opinion  between 
authorities,  which  at  times  are  quite  bewildering. 

The  views  of  the  author,  as  derived  from  his  own 
observation  of  the  behavior  of  cement  in  use  or  in  the 
laboratory,  have  been  stated  without  reserve,  and  free 
use  has  been  made  of  the  results  of  available  European 
investigations.  The  recommendations  of  the  recent 
commissions  appointed  in  Europe  for  the  study  of  the 
methods  of  testing  materials  are  fully  given  in  so  far 
as  they  relate  to  cement. 

The  various  tests  applied  for  determining  the  quality 
of  cement  are  discussed,  and  an  effort  is  made  to 
point  out  the  limitaticvis  within  which  they  may  be 
accepted  as  reliable  indications  of  value. 

A  chapter  is  given  upon  the  use  of  cement  in  mor- 
tar and  concrete,  and  a  number  of  sample  specifica- 
tions are  appended  for  the  purpose  of  showing  the 
present  practice  of  leading  American  engineers. 

F.  P.  S. 

ITHACA,  N.  Y.,  March,  1897. 

iii 

182027 


CONTENTS. 


CHAPTER    I. 
'HYDRAULIC  LIME. 

PAGE 

Art.  i.   Definition I 

"     2.  Chemical  Ingredients 3 

"     3.   Hydraulic  Index 7 

"    4.  Classification  of  Limes 8 

"    5.  Common  Lime 9 

"    6.   Hydraulic  Lime 13 

"     7.   Manufacture  of  Hydraulic  Lime 16 

"     8.   Grappicrs 19 

"    9.   Puzzolana 21 

CHAPTER    II. 
CLASSIFICATION  AND   CONSTITUTION  OF  CEMENT. 

Art.  10.  Classification  of  Cement 23 

1  n.  Manufacture  of  Cement 26 

"  12.  Portland  Cement 30 

'  13.  Natural  Cement 37 

"  14.  Slag-cement 42 

1  15.  Mixed  Cement 46 

'  16.  Grappiers  Cement 47 

'  17.  Sand-cement 48 

CHAPTER    III. 
THE  SETTING   AND  HARDENING  OF  CEMENT. 

Art.  18.   The  Setting  of  Cement 49 

"     19.   The  Hardening  of  Cement 50 


VI  CONTENTS. 

PAGE 

Art.  20.  Chemical  Theory 51 

"     21  Influence  of  Calcium  Sulphate 55 

"     22.  Influence  of  Calcium  Chloride 57 

' '     23.  Effect  of  Sand 60 

"     24.  Water  used  in  Gauging 61 

"     25.  Effect  of  Environment 64 

"     26.  Effect  of  Temperature 64 

"     27.  Effect  of  Age  upon  Cement 67 

"     28.  Effect  of  Fineness ,                            68 


CHAPTER    IV. 
THE  SOUNDNESS  OF  CEMENT. 

Art.  29.   Permanence  of  Volume 70 

"     30.   Free  Lime 72 

"     31.   Magnesia 74 

"     32.   Aluminate  of  Lime 77 

"     33.   Sulphur  Compounds 78 

"     34.   Exterior  Agencies So 

"     35.   Effect  of  Sea-water 82 

CHAPTER   V. 

METHODS  Or  TESTING  CEMENT. 

Art.  36    Object  of  Tests 85 

"     37.   Apparent  Density 88 

"     38.   Specific  Gravity 96 

"     39.  Tests  for  Fineness 103 

"     40.   Rate  of  Setting 105 

"     41.  Change  of  Temperature  during  Setting in 

CHAPTER    VI. 
TESTS  FOR   THE  STRENGTH  OF  MORTAR. 

Art.  42.   Methods  Employed 113 

"     43.   Form  of  Briquette    117 

"     44.   Quantity  of  Water  used  in  Gauging 120 

"     45.   Methods  of  Making  Briquettes 123 


CONTENTS.  Vli 

PAGE 

Art.  46.  Mechanical  Appliances  for  Making  Briquettes 129 

"     47.  Tensile  Tests 139 

"     48.  Compression  Tests 146 

"     49.  Transverse  Tests 151 

"     50.  Tests  of  Sand-mortar 153 

"     51.  Interpretation  of  Results 156 

CHAPTER   VII. 
TESTS  FOR  SOUNDNESS. 

Art.  52.  Ordinary  Tests 161 

"  53.   Measurement  of  Expansion 166 

"  54.   Accelerated  Tests 171 

"  55.   Kiln  Test 173 

"  56.  Steam  and  Hot-water  Test 176 

"  57.   Boiling  Test 180 

"  58.   Pressure  Test 183 

"  59.  Chloride  of  Calcium  Test 184 

"  60.  Value  of  Accelerated  Tests 185 

"  61.  Air-slaking , 193 

CHAPTER   VIII. 

SPECIAL   TESTS. 

Art.  62.  Test  of  Adhesive  Strength 195 

"  63.  Chemical  Analysis 199 

"  64.  Tests  for  Homogeneity 207 

"  65.  Abrasive  Tests 213 

"  66.  Tests  for  Porosity 215 

"  67.  Tests  for  Permeability 217 

"  68.  Frost  Tests    221 

"  69.  Tests  for  Yield  of  Mortar 222 

'•  70.  Tests  of  Sand 223 

CHAPTER    IX. 

CEMENT-MORTAL  AND  CONCRETE. 

Art.  71.  Sand  for  Mortar 224 

"     72.   Proportioning  Mortar 227 


Vlii  CONTENTS. 

PAGE 

Art.  73.  Gauging  Mortar 229 

"  74.   Preparation  of  Concrete 231 

"  75.  Yield  of  Mortar  and  Concrete 235 

"  76.   Mixtures  of  Lime  and  Cement 237 

"  77.  The  Freezing  of  Mortar 238 

"  78.   Porosity  and  Permeability  of  Mortar 241 

"  79.   Expansion  and  Contraction  of  Mortar 244 

"  80.   Effect  of  Retempering  Mortar. 245 


APPENDIX. 

SPECIFIC  A  TIONS  FOR    THE  RECEPTION  OF  CEMENT. 

A.  Specifications   of   the    Pennsylvania  Railroad;  Joseph  T. 

Richards,  Engineer  Maintenance  of  Way 249 

B.  Specifications  of  the   Canadian  Pacific   Railway;   Mr.   P. 

Alex.  Peterson,  Chief  Engineer 252 

C.  Extracts    from    Specifications    for    Furnishing     Portland 

Cement  for  Wallabout  Improvement,  Brooklyn;  Mr.  W. 

E.  Belknap,  Engineer .253 

D.  Specifications  for  Municipal  Work  in  St.  Louis;  Mr.  M.  L. 

Holman,  Water  Commissioner 259 

E.  Specifications  for  Municipal  Work  in  Philadelphia;  Mr.  G. 

S.  Webster,  Chief  Engineer,  Bureau  of  Surveys 261 


HYDRAULIC   CEMENT. 


CHAPTER    I. 
HYDRAULIC   LIME. 

ART.  1.     DEFINITION. 

LlME  is  the  name  commonly  applied  to  the  product 
obtained  by  the  calcination  of  limestone.  The  lime- 
stones employed  differ  greatly  in  composition,  and  the 
properties  of  the  limes  obtained  from  them  vary  with 
the  nature  and  proportions  of  the  substances  combined 
in  them. 

When  the  limestone  is  composed  of  nearly  pure 
carbonate  of  lime,  the  clinker  resulting  from  the  burn- 
ing, known  as  quicklime,  possesses  the  property  of 
breaking  up,  or  slaking,  upon  being  treated  with  a 
sufficient  quantity  of  water.  The  slaking  of  lime  is 
due  to  its  rapid  hydration  when  in  contact  with  water, 
and  the  process  is  accompanied  by  a  considerable  in- 
crease in  the  volume  of  the  mass  of  lime  and  by  a  rise 
in  temperature.  If  the  quantity  of  water  be  only 
sufficient  to  cause  the  hydration  of  the  lime,  the  quick- 


2  HYDRAULIC  CEMENT. 

lime  is  reduced  to  a  dry  powder;  while  if  the  water  be 
in  excess  it  becomes  a  paste. 

The  slaked  lime  thus  formed  possesses  the  further 
property,  when  mixed  to  a  paste  with  water  and  allowed 
to  stand  in  the  air,  of  hardening  and  firmly  adhering 
to  any  surface  with  which  it  may  be  in  contact.  This 
hardening  of  common  limes  will  take  -place  only  when 
exposed  to  the  air  and  allowed  to  become  dry. 

When  lime  is  nearly  pure  and  its  activity  is  very 
great  it  is  known  as  fat  lime. 

If  the  lime  have  mixed  or  in  combination  with  it 
considerable  percentages  of  impurities  of  an  inert 
character,  which  act  as  an  adulteration  to  lessen  the 
activity  of  the  lime,  causing  a  partial  loss  of  the  prop- 
erty of  slaking  and  also  diminishing  its  power  of  hard- 
ening, it  is  known  as  meagre  lime. 

When  the  impurities  in  the  lime  are  composed 
mainly  of  silica  and  alumina,  they  may,  while  lessening 
or  destroying  its  property  of  slaking,  impart  to  it  the 
power  of  hardening  under  water  and  of  setting  without 
reference  to  the  presence  of  air. 

When  the  proportions  of  the  hydraulic  ingredients 
are  such  that  the  material  possesses  the  property  of 
hardening  in  water,  without  having  entirely  lost  that 
of  slaking,  the  material  is  known  as  hydraulic  lime. 

If  the  acquirement  of  hydraulic  properties  has  been 
accompanied  by  an  entire  loss  of  the  property  of  slak- 
ing, the  product  is  hydraulic  cement. 

Hydraulic  limes  and  cements  may  be  made  either 
by  burning  limestones  containing  the  proper  propor- 
tions of  hydraulic  ingredients,  in  which  case  they  are 
known  as  natural  limes  or  cements,  or  by  the  admix- 


HYDRAULIC   LIME.  3 

ture  of  material  containing  such  ingredients  to  the 
limestone  before  burning,  or  to  the  lime  afterward,  in 
which  case  they  are  known  as  artificial  limes  or 
cements. 

The  materials  used  in  the  manufacture  of  lime  and 
cement  vary  widely  in  different  localities,  and  the 
resulting  products  differ  greatly  in  their  properties, 
being  affected  both  by  the  composition  of  the  raw 
materials  and  by  the  manipulation  given  them  during 
the  process  of  manufacture.  Because  of  this  variation 
in  the  character  of  the  material,  it  is  extremely  diffi- 
cult to  formulate  any  general  laws  governing  its  prop- 
erties, or  to  devise  any  system  of  testing  which  shall 
give  an  accurate  determination  of  value. 

Hydraulic  limes  are  used  quite  extensively  in 
Europe,  but  are  not  made  to  any  extent  in  this  coun- 
try. The  American  cement  industry  is,  however,  a 
very  important  one.  Natural  cements  are  manufac- 
tured in  immense  quantities,  and  the  production  of 
Portland  cement  is  rapidly  growing  to  large  propor- 
tions, although  considerable  of  high-grade  foreign 
cement  is  still  imported. 

ART.  2.     CHEMICAL  INGREDIENTS. 

The  most  important  ingredients  of  hydraulic  lime- 
stones, in  addition  to  the  carbonate  of  lime,  are  usually 
alumina,  silica,  oxide  of  iron,  and  magnesia.  They 
commonly  contain  also  small  quantities  of  sulphuric 
acid,  phosphoric  acid,  oxide  of  manganese,  potash, 
soda,  bituminous  or  carbonaceous  matter,  organic  sub- 
stances and  water.  The  lime  after  burning  may  also 


4  HYDRAULIC   CEMENT. 

contain  small  particles  of  cinders  from  the  combus- 
tibles employed. 

The  volatile  substances  are  without  effect  upon  the 
lime  because  they  disappear  in  burning.  A  small 
percentage  of  carbonic  acid  and  water  which  escapes 
being  driven  off  in  the  burning  or  is  afterward  absorbed 
from  the  air  will  appear  in  the  lime.  If  this  quantity 
of  carbonic  acid  be  large,  it  indicates  either  that  the 
burning  has  been  incomplete  or  that  the  lime  has 
become  carbonated  by  subsequent  exposure.  The 
energy  of  the  lime  is  thus  diminished,  the  portion  of 
lime  in  combination  with  the  carbonic  acid  being 
rendered  inert. 

Silica  is  undoubtedly  the  most  important  element 
in  rendering  lime  hydraulic  and  is  always  present. 
When  in  the  form  of  silicious  sand  not  attacked  by 
acids  it  is  unaffected  by  the  burning  and  remains  as 
inert  material  in  the  product.  It  is  only  that  portion 
of  the  silica  which  is  present  in  a  condition  to  be  re- 
duced in  the  burning  and  combine  with  the  lime 
which  is  of  value  in  imparting  hydraulic  properties  to 
the  lime. 

Alumina  is  an  important  element  in  hydraulic  lime, 
although  not,  as  seems  to  be  the  case  with  silica,  an 
essential  to  its  hydraulicity.  Vicat  found  that  alumina 
without  silica  would  not  render  lime  hydraulic. 
When,  however,  it  is  combined  with  silica  it  becomes 
one  of  the  active  elements  in  the  setting  and  harden- 
ing of  hydraulic  limes  and  cements,  provided  it  be  not 
present  in  too  large  proportions.  When  in  excess  of 
about  one  part  alumina  to  two  parts  silica,  it  is  claimed 
that  the  surplus  re-mains  inert  in  the  lime  and  detracts 


HYDRAULIC   LIME.  5 

from  its  energy.  This,  however,  very  rarely  happens 
in  practice. 

Oxide  of  Iron  is  commonly  thought  to  be  without 
influence  upon  the  hydraulicity  of  lime,  although 
there  is  some  question  concerning  it.  Like  alumina, 
it  confers  no  hydraulic  properties  when  alone,  and  it 
is  probably  always  inert. 

Magnesia  seems  to  act  quite  differently  as  the  con- 
ditions under  which  it  is  present  vary,  and  its  real 
action  in  most  cases  is  in  considerable  doubt.  Vicat 
made  hydraulic  limes  by  burning  carbonate  of  mag- 
nesia with  fat  lime,  thus  showing  that  the  magnesia 
alone  might  impart  hydraulic  properties  to  the  lime. 
It  has  also  been  shown  by  Mr.  H.  St.  Claire  Deville 
that  the  oxide  of  magnesium  by  itself  is  sometimes  an 
hydraulic  material  and  sets  under  water.  Other  ex- 
periments have  seemed  to  indicate  that  magnesia 
might  act  like  alumina,  and  replace  that  element  in 
forming  an  hydraulic  material  with  silica  and  lime. 
These  results  may  possibly  all  be  due  to  the  hydraulic 
properties  of  the  magnesium  oxide  and  independent 
of  any  action  of  the  magnesia  upon  the  lime. 

The  silicates  and  aluminates  of  magnesia  also  have 
the  property  of  hardening  underwater  like  the  similar 
salts  of  lime,  and  in  some  cements  a  portion  of  the 
lime  which  would  otherwise  be  required  seems  to  be 
replaced  by  magnesia.  The  action  in  these  instances 
is  not  definitely  known,  and  there  is  a  difference  of 
opinion  amongst  authorities  concerning  it,  some  think- 
ing that  the  magnesia  acts  like  lime,  others  that  it  is 
inert  and  does  not  contribute  to  the  energy  of  the 
material.  In  view  of  the  activity  of  the  magnesian 


6  HYDRAULIC   CEMENT. 

salts  when  alone,  it  seems  reasonable  to  suppose  that 
they  have  a  similar  effect  in  the  magnesian  cements. 

The  activity  of  magnesia  in  hydraulic  material 
depends  largely  upon  the  temperature  at  which  it  is 
burned,  and  in  the  experiments  which  have  demon- 
strated its  hydraulic  properties  it  has  been  found  that 
too  high  temperature  destroys  these  properties.  This 
possibly  accounts  for  many  of  the  contradictory  results 
obtained  by  different  investigators  with  these  salts. 
This  also  is  true  in  a  less  degree  with  the  lime  salts, 
which  may  sometimes  be  rendered  inert  by  too  high 
temperature. 

SulpJiuric  Acid  occurs  in  some  limestones  as  sulphate 
of  lime,  and  sulphur  also  sometimes  occurs  as  a  sul- 
phide, usually  of  iron.  During  the  burning  the  sul- 
phide may  become  transformed  into  sulphate,  and 
either  or  both  forms  may  result  in  the  final  product. 
Experience  seems  to  indicate  that  the  sulphate  is,  in 
general,  a  deleterious  substance,  likely  to  affect  the 
durability  of  mortar  made  from  lime  in  which  it 
occurs.  The  sulphide,  however,  is  supposed  to  in- 
crease the  hydraulic  properties  of  the  material, 
although  its  action  is  doubtful.  In  Europe  it  is  com- 
mon to  limit  the  percentage  of  sulphur  or  sulphuric 
acid  which  may  be  present  in  the  lime. 

Phosphoric  Acid  occurs  in  very  small  quantities  in 
material  of  this  character,  and  is  thought  to  have  no 
action  other  than  that  of  combining  with  a  small 
quantity  of  lime,  which  is  thus  rendered  inert. 

Oxide  of  Manganese  is  comparatively  unimportant, 
as  the  quantity  present  is  always  too  small  to  have 
any  considerable  effect  upon  the  properties  of  the 


HYDRAULIC   LIME.  7 

lime.      It  has  been  supposed  by  some  authorities  to 
have  strong  hydraulic  properties. 

The  Alkalies  contained  in  the  limestone  act  as  a 
flux  during  the  burning,  causing  the  chemical  reactions 
to  take  place  more  readily  and  completely.  The 
small  amount  which  ordinarily  ocurs  in  lime  and 
cement  is  unimportant  in  its  effect,  the  alkali  being 
gradually  dissolved  out  of  the  mortar. 

ART.  3.     HYDRAULIC  INDEX. 

The  hydraulic  activity  of  a  lime  or  cement,  that  is, 
its  ability  to  harden  under  water,  depends  primarily 
upon  the  relative  proportions  of  the  hydraulic  in- 
gredients and  of  lime.  Silica  and  alumina  are  consid- 
ered to  be  the  effective  hydraulic  ingredients,  and  it 
is  common  to  designate  the  ratio  of  the  sum  of  the 
weights  of  silica  and  alumina  to  that  of  lime  in  the 
material  its  hydraulic  index. 

The  hydraulic  index  gives,  therefore,  within  certain 
limits,  a  measure  of  the  hydraulicity  of  the  various 
classes  of  limes.  It  is  to  be  remembered,  however, 
that  there  are  other  factors  to  be  considered  in  judg- 
ing of  the  action  of  a  lime  than  this  simple  proportion. 
The  other  ingredients  may  by  their  combinations 
withdraw  portions  of  the  active  elements  so  as  to 
modify  the  effective  ratio  between  them,  while  the 
activity  of  the  lime  depends  largely  upon  the  state  of 
combination  in  which  the  active  elements  exist.  This 
is  not  shown  by  analysis,  and  may.  be  greatly  modified 
by  the  manipulation  given  the  material  during  manu- 
facture. 


HYDRAULIC   CEMENT. 


ART.  4.     CLASSIFICATION  OF  LIMES. 

Limes  may  be  classified  according  to  their  hydraulic 
indices,  or  according  to  the  rate  of  hardening  under 
water. 

Limes  with  hydraulic  index  less  than  10/100  pos- 
sess little  if  any  hydraulic  properties,  and  are  known 
as  common  limes,  which  may  be  either  fat  limes  or 
meagre  limes  according  to  the  proportion  of  inert 
material  contained  by  them. 

When  the  hydraulic  index  is-  between  10/100  and 
20/100  the  lime  is  known  as  feebly  hydraulic  and 
may  require  from  12  to  20  days  to  harden  under 
water.  Hydraulic  lime  proper  includes  that  of  index 
varying  from  about  20/100  to  40/100.  These  may 
harden  in  2  to  8  or  10  days,  the  more  rapid  ones 
being  sometimes  classed  as  eminently  hydraulic. 

When  the  hydraulic  index  is  between  about  40/100 
and  60/100  the  lime  is  of  the  class  known  as  limiting 
lime.  These  limes  have  not  the  characteristics  of 
hydraulic  lime,  but  form  the  boundary  between  the 
limes  proper  and  the  cements,  losing  the  property  of 
slaking,  and  as  a  general  thing  not  possessing  a  suffi- 
cient quantity  of  the  hydraulic  ingredients  to  make  a 
safe  natural  cement.  When  burned  at  a  low  tem- 
perature it  may  give  hydraulic  lime  of  rather  poor 
quality,  and  when  properly  treated  and  burned  at  a 
high  temperature  it  makes  good  Portland  cement. 
From  material  with  an  index  of  65/100  to  iT?ff°i5  are 
obtained  most  of  the  common  natural  cements.  With 
hydraulic  index  of  i^  to  3TQy°o>  the  material  yielded 


HYDRAULIC   LIME.  9 

by  burning  is  known  as  meagre  cement,  usually  a  weak 
material  of  little  value  as  a  cement. 

The  material  of  hydraulic  index  S^A  m^y  be 
puzzolana,  which  has  not  the  properties  of  cement, 
but  when  mixed  with  fat  lime  renders  the  lime 
hydraulic. 

The  above  divisions  are  all  more  or  less  arbitrary, 
and  there  are  no  sharp  lines  between  the  classes,  which 
merge  into  and  overlap  each  other.  The  character  of 
the  material  is  also  affected  by  other  factors  than  the 
hydraulic  index,  and  classification  by  this  method  is  by 
no  means  invariable,  material  of  one  class  frequently 
behaving  like  that  of  another  class.  It  is  difficult  to 
determine  at  exactly  what  point  lime  begins  to  be 
hydraulic,  but  when  it  requires  a  month  or  more  to 
harden  under  water  it  is  usually  considered  as  being 
non-hydraulic. 

In  determining  the  rate  of  hardening  of  limes  there 
are  so  many  external  circumstances  which  may  affect 
the  result  that  there  is  always  chance  for  error,  which 
causes  classification  by  that  method  to  be  somewhat 
uncertain.  Variation  in  temperature  has  always  an 
important  effect  upon  the  rate  of  hardening. 

ART.  5.     COMMON  LIME. 

Common  lime  is  such  as  does  not  possess  hydraulic 
properties.  It  is  divided  into  fat  or  rich  lime  and 
meagre  lime,  according  to  the  quantity  of  impurities 
of  an  inert  character  it  may  contain.  When  made 
into  a  paste  and  left  in  air  it  slowly  hardens.  The 
process  of  hardening  consists  in  the  gradual  formation 


IO  HYDRAULIC   CEMENT. 

of  carbonate  of  lime  through  the  absorption  of  car- 
bonic acid  from  the  air,  accompanied  by  the  crystalli- 
zation of  the  mass  of  hydrated  lime  as  it  gradually 
dries  out.  In  common  lime  the  final  hardening  takes 
place  very  slowly,  working  inward  from  the  surface, 
as  it  is  dependent  upon  contact  of  the  mortar  with  the 
air.  When  the  lime  is  nearly  pure  the  resulting  car- 
bonate is  likely  to  be  somewhat  soluble,  and  conse- 
quently to  be  injured  by  exposure.  Nearly  all  limes, 
however,  contain  small  percentages  of  silica  and 
alumina,  and  these  ingredients,  even  when  in  quanti- 
ties too  small  to  render  the  lime  hydraulic,  impart  a 
certain  power  to  set,  causing  the  hardening  to  take 
place  with  greater  rapidity  and  without  the  same 
dependence  upon  contact  with  air.  It  also  renders 
the  material  less  soluble  and  more  durable  in  exposed 
situations. 

Limes  containing  but  a  small  amount  of  impurities 
consist  mainly  of  calcium  oxide,  which  is  very  caustic 
and  becomes  hydrated  very  rapidly  when  brought  into 
contact  with  water.  This  hydration,  or  slaking,  pro- 
duces a  rise  in  temperature  and  an  increase  in  volume, 
which  vary  in  amount  according  to  the  purity  of  the 
lime,  the  volume  being  doubled  or  tripled  for  good 
fat  lime. 

The  common  method  of  slaking  consists  in  covering 
the  quicklime  with  water,  using  two  or  three  times  the 
volume  of  the  lime.  This  method  is  known  as  drown- 
ing. The  lime  is  usually  spread  out  in  a  layer,  per- 
haps 6  or  8  inches  thick,  in  a  mixing-box,  the  water 
poured  over  it  and  allowed  to  stand.  Sufficient  time 
must  be  allowed  for  all  of  the  lumps  to  be  reduced. 


HYDRAULIC   LIME.  II 

When  the   lime  contains    much    foreign  matter,    the 
operation  frequently  requires  several  days. 

Too  great  a  quantity  of  water  is  to  be  avoided,  the 
amount  necessary  being  such  as  will  reduce  the  lime 
after  slaking  to  a  thick  pasty  condition.  All  the  water 
should  be  added  at  once,  as  the  addition  of  water  after 
the  hydration  is  in  progress  causes  a  lowering  of  tem- 
perature and  checks  the  slaking.  For  the  same 
reason,  the  lime  should  be  covered  after  adding  water, 
and  not  stirred  or  disturbed  until  the  slaking  is  com- 
pleted. The  covering  is  commonly  effected  by  spread- 
ing a  layer  of  sand  over  the  lime;  the  sand  being 
afterward  used  to  mix  with  it  in  making  the  mortar. 

A  second  method  of  slaking  is  sometimes  employed 
having  for  its  object  the  reduction  of  the  slaked  lime 
to  powder  and  known  as  slaking  by  immersion. 

Slaking  by  immersion  is  accomplished  in  two  ways. 
By  the  first  method,  the  lime  is  suspended  in  water  in 
baskets  for  a  brief  period  to  permit  the  absorption  of 
the  necessary  water,  after  which  it  is  removed  and 
covered  until  the  slaking  takes  place  and  the  lime  falls 
to  powder. 

By  the  second  method,  sprinkling  is  substituted  for 
immersion  proper,  the  lime  being  placed  in  heaps  and 
sprinkled  with  the  necessary  quantity  of  water,  then 
covered  with  sand  and  allowed  to  stand. 

The  difficulty  in  using  these  methods  is  to  get  just 
the  right  quantity  of  water  to  make  the  slaking  com- 
plete. Lime  so  slaked  may  be  barreled  and  shipped 
in  form  of  powder. 

Spontaneous  Slaking is  also  sometimes  resorted  to; 


12  HYDRAULIC  CEMENT. 

it  consists  in  exposing  the  lime  to  the  air  until  slaking 
is  effected  by  absorption  of  moisture. 

Lime  slaked  by  immersion  swells  less  than  when 
slaked  by  drowning  and  requires  less  water  to  form 
into  a  paste.  Slaked  lime,  either  as  powder  or  paste, 
may  be  kept  indefinitely  if  protected  from  the  air. 

Lime  is  commonly  sold  as  quicklime,  and  should  be 
in  lumps  and  not  air-slaked.  When  it  is  old  and  has 
been  exposed  to  the  air,  it  is  likely  to  have  absorbed 
both  moisture  and  carbonic  acid,  thus  becoming  less 
active,  the  portion  combined  with  the  carbonic  acid 
being  inert.  A  simple  test  of  the  quality  of  quick- 
lime is  to  immerse  a  lump  for  a  minute,  then  place  in 
a  dish  and  observe  whether  it  swells,  cracks,  and  dis- 
integrates with  a  rise  of  temperature. 

Slaking  some  days  in  advance  of  use  is  desirable  in 
order  to  insure  the  complete  reduction  of  the  lime, 
and  it  is  quite  common  to  slake  lime  much  longer 
before  it  is  to  be  used. 

The  swelling  of  lime  has  been  found  to  be  increased 
by  slaking  with  steam  instead  of  water,  and  slaking 
has  been  found  by  M.  Candlot  to  be  accelerated  by 
the  addition  to  the  water  of  a  small  quantity  (2%  to  6#) 
of  chloride  of  calcium  or  chloride  of  magnesium. 

Common  lime  is  ordinarily  used  in  construction  as 
a  mortar,  mixed  with  sand.  The  quantity  of  lime  in 
the  mortar  should  be  just  sufficient  to  fill  the  voids  in 
the  sand,  without  leaving  any  part  formed  entirely  of 
lime.  Mortar  of  rich  lime  shrinks  on  hardening,  while 
masses  composed  entirely  of  lime  on  the  interior  are 
likely  to  remain  soft,  so  that  an  excess  of  lime  may  be 
an  element  of  weakness.  If  too  little  lime  be  used, 


HYDRAULIC   LIME.  13 

the  mortar  may  be  porous  and  weak.  The  propor- 
tions ordinarily  required  are  between  i  part  lime  to  2 
parts  sand,  and  I  part  lime  to  3  parts  sand. 

Mortar  of  common  lime  should  not  usually  be  em- 
ployed in  heavy  masonry  or  in  damp  situations. 
Where  the  mass  of  masonry  is  large,  the  lime-mortar 
will  become  hardened  only  with  great  difficulty  and 
after  a  long  time.  The  penetration  of  the  final  in- 
duration due  to  the  absorption  of  carbonic  acid  is  very 
slow.  The  observations  of  M.  Vicat  showed  that  car- 
bonization extended  only  a  few  millimeters  the  first 
year  and  afterward  more  slowly.  The  induration  of 
the  lime  along  the  surfaces  of  contact  with  a  harder 
material,  when  used  in  masonry,  is  usually  more  rapid 
than  in  the  interior  of  the  mass  of  lime  itself,  and 
hence  the  strength  of  adhesion  to  stone  or  brick  is 
often  greater  than  that  of  cohesion  between  the  par- 
ticles of  mortar. 

Meagre  limes  are  similar  in  action  to  fat  limes,  but 
less  energetic.  They  swell  feebly  in  slaking  and  with 
slight  change  in  temperature.  The  mortar  hardens 
like  that  of  fat  lime,  but  cracks  less  and  contracts  less. 
Meagre  limes  proper,  those  containing  so  much  inert 
matter  as  to  materially  reduce  the  energy,  are  not 
commonly  employed  in  construction. 

ART.  6.     HYDRAULIC  LIME. 

Hydraulic  lime  is  obtained  by  burning  limestone 
containing  silica  and  alumina  in  sufficient  quantity  to 
impart  the  ability  to  harden  under  water.  The  hy- 
draulic elements  are  present  in  such  quantities  that 


14  HYDRAULIC   CEMENT. 

they  combine  with  a  portion  of  the  lime,  forming  sili- 
cates and  aluminates  of  lime,  leaving  the  remainder  as 
free  lime  in  an  uncombined  state. 

When  treated  with  water  the  free  lime  is  slaked, 
the  action  being  much  less  energetic  than  that  of  fat 
lime  and  varying  in  intensity  with  the  quantity  of 
hydraulic  ingredients. 

The  quantity  of  free  lime  in  the  material  is  depend- 
ent upon  the  degree  of  burning,  as  well  as  upon  the 
amount  of  lime  contained  by  the  stone.  If  the  stone 
be  underburned,  the  combination  of  the  hydraulic  ele- 
ments with  the  lime  is  not  complete,  and  more  of  the 
lime  remains  in  a  free  state.  For  this  reason  a  stone 
of  high  hydraulic  index  may  give  a  lime  when  under- 
burned,  but  become  unslakable  when  burned  at  a  high 
temperature,  as  in  the  case  of  the  limiting  limes.  The 
best  limes  are  usually  those  which  can  be  burned  at  a 
high  temperature  to  complete  the  chemical  combina- 
tions. 

t  is  necessary  that  sufficient  free  lime  be  present 
to  cause  the  lime  to  slake  properly,  but  it  is  desirable 
also  that  the  quantity  of  uncombined  lime  be  as  small 
as  possible,  as  the  setting  properties  are  due  to  the 
silicates  and  aluminates,  while  the  hydrated  lime 
remains  inert  durinp1  the  initial  hardening  of  the 
mortar. 

According  to  Professor  Le  Chatelier,  limestone  for 
hydraulic  lime  should  contain  but  little  alumina,  as  the 
aluminates  are  hydrated  during  the  slaking  of  the  lime 
and  become  inert,  while  the  silicates  are  not  affected, 
the  heat  of  the  slaking  preventing  their  hydration. 


HYDRAULIC   LIME.  1 5 

The  following  is  given  as  an  average  analysis  of  the 
best  French  hydraulic  lime: 

Silica 22 

Alumina 2. 

Oxide  of  iron I. 

Lime 63. 

Magnesia.  ....*.... 1.5 

Sulphuric  acid 0.5 

Water.  .  10.0 


100 


It  is  important  that  the  slaking  be  very  thorough, 
as  the  presence  of  unhydrated  free  lime  in  the  mortar 
while  hardening  is  an  element  of  danger  to  the  work. 
Any  lime  becoming  hydrated  after  the  setting  of  the 
mortar  may,  by  its  swelling,  cause  distortion  and  per- 
haps disintegration  of  the  mortar. 

Hydraulic  lime  is  used  in  the  same  manner  as  fat 
lime,  being  mixed  with  sand  to  a  paste.  When  in  the 
air  hydraulic  lime  acts  like  common  lime,  dries",  har- 
dens, and  slowly  absorbs  carbonic  acid.  It  contracts 
and  cracks  when  without  sand,  but  much  less  than  fat 
lime.  In  water,  or  in  damp  situations,  the  action  of 
the  two  are  altogether  different.  The  hydraulic  lime 
then  hardens  more  or  less  rapidly.  In  running  water 
a  small  amount  of  the  lime  is  at  first  dissolved,  but 
this  is  soon  arrested  as  the  hardening  progresses. 

Hydraulic  lime  is  commonly  slaked  at  the  manufac- 
tory and  shipped  in  form  of  powder.  It  may  be  kept, 
without  injury,  in  this  form  by  covering  and  protect- 
ing from  the  air. 


l6  HYDRAULIC   CEMENT. 

ART.  7.     MANUFACTURE  OF  HYDRAULIC  LIME. 

The  manufacture  of  hydraulic  lime  as  commonly 
carried  on  in  Europe  consists,  after  the  quarrying  of 
the  rock,  of  burning,  slaking,  and  bolting  the  material. 
As  already  stated,  it  is  usually  slaked  at  the  works  and 
sold  in  the  form  of  powder. 

The  varieties  of  furnaces  used  in  burning  are  quite 
numerous,  but  may  be  divided  into  those  in  which  the 
stone  is  burned  in  contact  with  the  fuel,  and  those  in 
which  the  fire  is  outside  the  chamber  in  which  the 
burning  takes  place. 

Furnaces  of  the  first  class  have  been  more  generally 
employed,  and  are  claimed  (Candlot,  Ciment  et  Chaux 
hydrauliques,  p.  7)  to  be  preferable  from  the  point  of 
view  of  the  uniformity  of  product.  Continuous  fur- 
naces are  commonly  used.  The  furnace  is  filled  by 
placing  alternate  layers  of  combustible  and  limestone. 
When  full  it  is  lighted  at  the  bottom,  and  as  the  mass 
settles,  new  layers  of  material  are  added  at  the  top, 
while  the  burned  lime  is  drawn  out  at  the  bottom,  the 
furnace  being  kept  in  continuous  operation.  The 
rapidity  of  burning  is  controlled  by  dampers  and  the 
movable  cover  at  the  top. 

In  furnaces  of  the  second  class,  the  flame  and  gases 
of  combustion  are  passed  through  the  stone,  which  is 
not  in  direct  contact  with  the  fuel. 

The  regulation  of  a  furnace  to  secure  the  proper 
degree  of  burning  is  a  matter  requiring  skill  and  ex- 
perience, and  demanding  the  close  attention  of  the 
attendant.  The  lime  must  be  completely  burned,  but 
not  overburned.  The  character  of  the  limestone 


HYDRAULIC   LIME.  I/ 

determines  the  amount  of  burning  necessary.  A  lime 
of  low  hydraulic  index  may  be  burned  at  a  much 
higher  temperature  than  one  of  high  index.  When 
the  limestone  is  irregular  in  character  it  will  not  burn 
evenly,  but  the  parts  of  high  index  will  be  vitrified 
before  that  of  low  index  is  properly  burned.  The 
burning  is  accelerated  when  the  stone  is  moist,  and 
stone  fresh  from  the  quarry  is  preferred  to  that  which 
has  been  exposed  until  the  hygrometric  water  has 
been  evaporated. 

The  chemical  phenomena  of  the  burning  of  lime  are 
approximately  as  follows:  The  hygrometric  water  is 
first  driven  off.  The  carbonate  of  lime  is  next  de- 
composed. Then  the  clay  is  dehydrated  and  decom- 
posed, and  the  combination  of  the  silica  and  alumina 
with  the  lime  takes  place.  The  temperatures  required 
to  effect  these  changes  depend  upon  the  composition. 
The  decomposition  of  the  carbonate  of  lime  takes 
place  at  a  lower  temperature  in  presence  of  silica,  and 
hence  silicious  limestones  are  burned  at  a  comparatively 
low  temperature  maintained  for  a  considerable  time, 
while  argillaceous  limestones  require  a  higher  tem- 
perature maintained  for  a  shorter  period.  According 
to  M.  Bonnami,  the  carbonate  of  lime  is  commonly 
decomposed  at  about  440°  C.,  while  the  clay  is  dehy- 
drated and  decomposed  at  above  700°  C.,  and  the 
silicates  and  aluminates  of  lime  are  then  formed.  If  a 
temperature  intermediate  between  these  points  be 
maintained  for  a  considerable  time,  the  result  will  be 
the  decomposition  of  the  carbonate  of  lime,  leaving 
caustic  lime  mixed  with  insoluble  clay. 

The  slaking  of  hydraulic  lime  is  commonly  accom- 


18  HYDRAULIC   CEMENT. 

plished  by  sprinkling,  as  mentioned  in  Art.  5.  The 
lime  after  coming  from  the  furnace  is  spread  in  layers 
4  to  8  inches  deep  in  the  slaking-chambers.  It  is 
then  sprinkled  so  that  all  of  the  quicklime  is  well 
moistened;  from  "]%  to  io#  of  water  is  commonly 
required.  When  the  lime  is  wet  it  is  thrown  into 
large  heaps  and  left  for  a  sufficient  time  for  the  slaking 
to  be  completed.  The  time  required  varies  with  the 
hydraulic  index  and  the  degree  of  burning.  Limes 
of  high  index  may  require  15  or  20  days.  When  the 
index  and  degree  of  burning  increase  together,  the 
lime  soon  becomes  unslakable. 

In  slaking,  the  object  is  to  obtain  the  complete 
hydration  of  the  uncombined  lime  without  causing  any 
change  in  the  silicates.  To  accomplish  this  the  slaking 
must  take  place  at  a  high  temperature.  The  heat  of 
slaking  volatilizes  the  surplus  moisture  and  prevents 
the  hydration  of  the  silicates.  If  the  temperature  be 
too  low,  the  lime  may  partially  harden  during  slaking 
and  the  portion  of  silicate  which  is  hydrated  becomes 
inert.  If  the  lime  be  imperfectly  slaked,  the  free  lime 
left  in  the  material  may  cause  injury  to  the  mortar 
after  hardening.  Lime  so  affected  will  set  more 
quickly  than  it  would  if  sound,  but  afterward  is  likely 
to  swell  and  crack. 

Steam  is  sometimes  used  for  slaking  instead  of 
water,  and  is  said  by  M.  Le  Chatelier  to  act  more 
rapidly  upon  the  lime  while  producing  no  effect  upon 
the  silicates. 

It  is  claimed  that  the  aluminates  are  hydrated  dur- 
ing the  slaking  of  the  lime,  being  readily  acted  upon 
by  steam,  and  hence  are  undesirable  in  hydraulic  lime. 


HYDRAULIC   LIME.  19 

After  the  lime  has  been  reduced  to  powder  by  slak- 
ing it  is  forced  through  sieves  which  permit  the 
passage  of  all  pulverized  particles,  but  hold  those  of 
appreciable  size,  including  the  underburned  rock  and 
the  overburned  parts  which  refuse  to  slake.  The 
lime  resulting  from  the  first  bolting  is  known  as  the 
flour  of  lime. 

ART.  8.     GRAPPIERS. 

The  residue  left  after  the  sifting  of  hydraulic  lime 
is  known  as  grappiers. 

It  differs  very  much  in  its  composition  in  various 
instances,  depending  upon  the  limestone  used  and  the 
manipulation  in  manufacture.  It  includes  the  under- 
burned  portions  of  the  limestone  and  the  overburned 
particles  which  will  not  slake.  When  the  burning  is 
thoroughly  done  and  the  limestone  used  regular  in 
composition,  the  proportion  of  unburned  particles  is 
small.  The  larger  part  of  the  residue  is  then  com- 
posed of  hard  material  more  rich  than  the  other  por- 
tions of  the  lime  in  silica  and  alumina,  obtained  from 
the  clay  which  is  disseminated  through  the  limestone 
or  formed  by  the  combination  of  the  cinders  of  com- 
bustion with  the  lime.  This  is  what  is  properly  meant 
by  the  term  grappiers. 

M.  Bonnami  found  in  his  investigations  that  the 
larger  part  of  the  grappiers  are  from  the  surfaces  of 
the  limestone  which  are  in  contact  with  the  combusti- 
ble during  the  burning,  and  due  to  the  silica  and 
alumina  of  the  cinders.  These  cinders  are  usually 
quite  aluminous. 


20 


HYDRAULIC   CEMENT. 


The  grappiers  are  ground  and  sifted  and  either 
added  to  the  lime  or  used  separately  as  cement. 

The  addition  of  ground  grappiers  to  hydraulic  lime 
has  the  effect  of  raising  the  hydraulic  index  of  the 
lime  and  increasing  its  activity,  and  offers  a  means  of 
controlling  to  a  certain  extent  the  properties  of  the 
lime.  In  this  case  the  mixture  between  the  lime  and 
the  grappiers  must  be  very  intimate  in  order  to  obtain 
a  homogeneous  material.  It  is  also  very  important 
that  the  lime  in  the  grappiers  be  entirely  slaked,  to 
prevent  the  introduction  of  free  lime  into  the  product. 
To  secure  this  the  grappiers  after  grinding  are  exposed 
to  the  air  for  a  considerable  time  before  using,  thus 
permitting  any  unslaked  particles  to  become  air-slaked. 

The  following  analyses  of  lime  and  grappiers  from 
the  great  works  at  Teil  are  given  by  Prof.  Durand- 
Claye  (Chimie  appliquee  a  1'art  de  1'ingenieur). 

ANALYSES   OF   LIME   AND   GRAPPIERS   FROM   TEIL. 


Slaked 
Lime. 

Merchantable 
Lime. 

Grappiers. 

Rejected 
Material. 

Silica 

Per  Cent. 

Per  Cent. 
2*1   qc 

Per  Cent. 
•31  8s 

Per  Cent. 

Alumina  and  iron  oxide. 

2-75 

3.10 

63  35 

4.25 
55  6° 

8.20 

45  25 

i   15 

I  20 

o  85 

6   Q5 

8  50 

7.  10 

2  60 

The  first  column  gives  the  ordinary  slaked  lime. 
Merchantable  lime  has  a  portion  of  powdered  grappiers 
added  to  augment  its  hydraulic  properties.  The  third 
column  gives  an  analysis  of  powdered  grappiers,  which 
is  sold  as  a  slow-setting  cement.  The  rejected  ira- 


HYDRAULIC   LIME.  21 

terial  is  a  calcareous  sand  which  has  puzzolanic  proper- 
ties. It  is  employed  with  cement  in  making  water- 
pipe,  brick,  etc. 

ART.  9.     PUZZOLANA. 

The  term  puzzolana  is  commonly  applied  to  a  class 
of  materials  which,  when  made  into  a  mortar  with  fat 
lime  or  feebly  hydraulic  lime,  impart  to  the  lime 
hydraulic  properties  and  cause  the  mortar  to  set  under 
water. 

Puzzolana  (or  pozzuolana)  proper  is  a  material  of 
volcanic  origin,  deriving  its  name  from  Pozzuoli,  a  city 
of  Italy  near  the  foot  of  Mount  Vesuvius,  where  its 
properties  were  first  discovered.  It  was  extensively 
used  by  the  Romans  in  their  hydraulic  constructions, 
being  pulverized  and  mixed  with  slaked  lime  and  a 
small  amount  of  sand  for  the  formation  of  hydraulic 
mortar. 

The  puzzolana  is  a  silicate  of  alumina  in  which  the 
silica  exists  in  a  state  easily  attacked  by  caustic  alka- 
lies, and  hence  readily  combines  with  the  lime  in  the 
morta- 

The  class  of  puzzolanas  also  includes  several  other 
materials  of  somewhat  similar  character. 

Trass  is  the  name  given  to  a  volcanic  material  found 
in  Germany  and  Holland,  much  resembling  puzzolana 
and  used  in  the  same  manner. 

Arcncs  is  a  sand  found  in  France  and  applied  to  the 
same  purpose.  It  is  quartzose  in  character  and  mixed 
with  clay  in  considerable  proportions;  from  1/4  to  3/4 
of  the  total  volume.  It  may  be  made  into  a  paste, 


22  HYDRAULIC   CEMENT. 

with  water,  which  will  harden  on  drying  out,  and  is 
sometimes  used  for  common  mortar  without  lime. 

Psammitcs  is  a  sandstone  consisting  of  grains  of 
quartz,  schist,  feldspar,  and  mica,  agglutinized  with  a 
variable  cement.  It  is  slaty  in  character  and  may  be 
worked  into  a  paste  with  water. 

Puzzolana  may  be  made  artificially  by  burning  clay, 
and  natural  ones  may  frequently  be  improved  by  burn- 
ing, which  has  the  effect  of  dehydrating  the  silicate  of 
alumina  of  which  they  are  mainly  composed  and  leav- 
ing it  in  condition  to  combine  readily  with  the  lime. 

Berthier  gives  the  following  analyses  of  average 
samples  of  puzzolanas: 

Trass.  Puzzolana. 

Silica 0.570  0.445 

Alumina 0.120  0.150 

Lime 0.026  0.088 

Magnesia o.oio  0.047 

Iron  oxide 0.050  o.  123 

Potash 0.070  0.014 

Soda o.oio  0.040 

Water,  etc 0.444  0.096 


CHAPTER    II. 
CLASSIFICATION  AND  CONSTITUTION  OF  CEMENT. 

ART.  10.     CLASSIFICATION  OF  CEMENT. 

HYDRAULIC  cements  may  be  classified  according  to 
the  method  of  manufacture  under  five  general  head- 
ings: Portland  cements,  natural  cements,  slag-cem- 
ents, mixed  cements,  and  grappiers  cements. 

The  term  Portland  Cement  is  commonly  used  to 
designate  hydraulic  cement  formed  by  burning  to  the 
point  of  vitrifaction  a  mixture  of  limestone  and  clay 
in  proper  proportions  and  reducing  the  resulting  mass 
to  powder  by  grinding.  The  cement  so  classified  is 
of  lower  hydraulic  index  than  the  other  cements,  and 
is  consequently  burned  at  a  higher  temperature. 
Portland  cement  is  usually  made  artificially  by  a  mix- 
ture of  limestone  and  clay  or  of  nearly  pure  lime- 
stone with  stone  of  high  index,  and  in  all  cases  the 
material  must  be  very  uniformly  incorporated  into  the 
mixture.  The  high  temperature  employed  in  burning 
and  the  necessity  of  reducing  the  raw  material,  whether 
natural  rock  or  artificial  mixture,  to  powder  before 
burning,  for  the  purpose  of  homogenizing  it,  may  be 
considered  the  distinctive  characteristics  of  this  class. 

The  conference  for  the  unification  of  methods  for 

23 


24  HYDRAULIC   CEMENT. 

testing  materials  at  Munich  *  propose  the  following 
additional  definition  of  Portland  cements:  "  They 
contain  a  minimum  of  1.7  parts  of  lime  per  unit  of 
hydraulic  substances.  The  addition  of  2%  by  weight 
of  foreign  matter  may  be  tolerated  in  the  manufacture 
of  Portland  cement,  with  the  view  of  augmenting  cer- 
tain important  qualities,  without  the  necessity  of 
changing  the  name." 

Natural  Cements  are  those  which  are  made  by  burn- 
ing limestones  less  rich  in  lime  than  those  giving 
hydraulic  limes  or  Portland  cement.  These  are 
burned  like  the  hydraulic  limes  without  pulverization 
of  the  raw  material,  and  require  a  much  lower  tem- 
perature in  burning  than  does  Portland  cement. 

This  class  includes  a  number  of  sub-classes  varying 
widely  in  composition  and  varlue.  In  Europe  they 
are  commonly  divided  into  quick-setting  natural 
cements,  frequently  called  Roman  Cement,  and  semi- 
slow-setting  cements,  known  sometimes  as  natural 
Portland  cement.  In  the  United  States  there  is  much 
greater  variety  in  the  materials  coming  within  this 
classification  and  much  confusion  in  their  nomencla- 
ture. They  are  most  commonly  designated  by  a 
name  derived  from  the  locality  in  which  they  are 
obtained,  and  this  seems  the  most  feasible  and  satis- 
factory method.  Thus,  Rosendale  cements  are  those 
from  the  region  of  the  lower  Hudson,  Lehigh  cements 
are  from  Southeastern  Pennsylvania,  Louisville  cem- 
ents from  the  Ohio  valley,  Potomac  and  James  River 

*  M6moires  de  la  Soci6te  des   Ingenicurs  Civils,  1891.   vol.   I. 

p.   112. 


CLASSIFICATION   AND   CONSTITUTION   OF   CEMENT.    2$ 

cements  from  the  corresponding  valleys,  while  Utica, 
Akron,  and  Milwaukee  are  names  indicating  the  loca- 
tion of  manufactories  of  particular  brands. 

The  term  American  Cement  has  sometimes  been 
applied  to  include  all  natural  cements  made  in  the 
United  States.  This,  however,  often  leads  to  con- 
fusion because  of  the  fact  that  other  than  natural 
cements  are  now  made  quite  extensively  in  this  coun- 
try, and  the  term  American  Portland  Cement  is  also  in 
common  use 

The  term  Rosendale  Cement  has  frequently  been 
given  a  general  meaning  and  used  as  synonymous  with 
natural  and  American  to  include  all  natural  cements. 
It  is,  however,  more  properly  restricted  to  the  cements 
of  the  district  in  which  it  was  first  applied,  and  there 
seems  to  be  no  good  reason  for  extending  it  to  include 
other  and  totally  different  material. 

Slag  Cement  or,  as  a  more  general  term,  Puzzolana 
Cement,  is  the  product  obtained  by  an  intimate  mix- 
ture of  slaked  lime  with  finely  pulverized  puzzolanic 
material,  commonly  blast-furnace  slag.  In  this  ma- 
terial the  hydraulic  ingredients  are  not  burned  with 
the  lime,  but  are  present  in  the  cement  in  a  mechanical 
mixture  only. 

Graf  piers  Cements  are  obtained  by  grinding  the  par- 
ticles which  are  not  pulverized  in  slaking  hydraulic 
lime. 

Mixed  Cement  is  the  name  given  in  Europe  to  an 
extremely  variable  class  of  products  obtained  by  mix- 
ing different  grades  of  cement  together,  or  by  mixing 
cement  with  other  material  for  the  purpose  of  impart- 
ing desired  properties. 


26  HYDRAULIC  CEMENT. 

ART.  11.     MANUFACTURE  OF  CEMENT. 

The  manufacture  of  hydraulic  cement  as  commonly 
practised  consists  of  four  operations,  viz.,  the  prepara- 
tion of  the  raw  material,  the  burning,  the  grinding, 
and  the  bolting. 

The  methods  of  preparing  the  raw  material  differ 
according  to  the  nature  of  the  material  and  the  method 
to  be  used  in  burning.  For  natural  cements  it  is 
usually  only  necessary  to  select  the  proper  portions  of 
the  rock  and  break  it  into  fragments  of  suitable  size 
for  introduction  into  the  furnace.  The  production  of 
good  cement  requires  the  use  of  homogeneous  material, 
and  care  must  be  used  to  prevent  the  introduction  of 
variable  rock  into  a  single  burning. 

For  Portland  cement  there  are  three  general 
methods  of  preparing  the  material,  in  all  of  which  it 
is  essential  to  good  results  that  the  various  ingredients 
be  very  carefully  proportioned  and  that  they  be  formed 
into  a  very  uniform  and  homogeneous  mixture  in 
order  to  facilitate  the  chemical  changes  in  all  parts  of 
the  material  during  the  burning.  The  first,  known  as 
the  wet  method,  consists  in  working  the  raw  materials 
into  an  intimate  mixture  by  reducing  to  a  paste  with 
water,  then  drying  into  bricks  which  may  be  stacked 
in  the  furnace  for  burning.  In  the  wet  process  proper 
a  large  excess  of  water  is  employed  and  afterward 
drawn  off.  In  the  semi- wet  process,  now  more  com- 
monly employed,  only  enough  water  is  used  to  reduce 
the  mixture  to  a  plastic  condition. 

The  second  method,  called  the  dry  method,  con- 
sists in  grinding  the  materials  together  dry  or  with  a 


CLASSIFICATION  AND   CONSTITUTION   OF   CEMENT.   2? 

very  small  quantity  of  water,  ana  making  bricks  of  the 
powder  by  subjecting  it  to  pressure  in  a  brick-machine. 
The  bricks  in  all  cases  require  thorough  drying  before 
being  placed  in  the  furnace. 

The  third  method  is  to  grind  the  dry  materials  into 
powder  and  burn  in  a  rotary  furnace  without  forming 
them  into  bricks,  or  to  mix  to  a  plastic  condition  and 
dry  in  small  lumps  on  the  circumference  of  a  drying- 
cylinder  for  burning  in  the  rotary  furnace. 

The  exact  proportioning  of  the  ingredients  and  the 
intimacy  of  their  incorporation  into  the  mixture  have 
very  important  bearing  upon  the  value  of  the  cement. 

The  materials  used  in  manufacturing  cement  differ 
greatly  in  different  localities,  and  the  method  employed 
depends  somewhat  upon  the  character  of  the  raw 
materials.  For  natural  cements  a  limestone  of  high 
hydraulic  index  is  usually  employed,  but  differing 
much  in  composition,  some  having  a  high  percentage 
of  alumina,  others  of  magnesia,  and  still  others  of  both. 
For  Portland  cements  the  most  common  materials  are 
a  fat  or  slightly  hydraulic  limestone  with  clay  or  shale, 
made  into  bricks  by  the  semi-wet  process.  Sometimes 
a  hydraulic  limestone  of  high  index  (such  as  is  used 
for  natural  cements)  is  mixed  with  a  fat  limestone, 
commonly  by  a  dry  method.  These  materials  are  also 
sometimes  used  by  the  method  of  double  calcination, 
that  is,  the  fat  limestone  is  first  burned  in  the  ordinary 
manner,  the  resulting  quicklime  is  slaked  and  bolted, 
after  which  the  slaked  lime  is  mixed  and  ground 
with  the  argillaceous  limestone,  the  object  being  to 
get  a  very  perfect  distribution  of  the  lime  through 
the  mixture. 


28  HYDRAULIC  CEMENT. 

The' method  of  double  calcination  is  also  sometimes 
employed  with  rock  containing  naturally  about  the 
right  proportions  of  hydraulic  ingredients  for  making 
Portland  cement.  The  composition  of  the  rock  being 
usually  somewhat  irregular,  it  is  lightly  burned  and 
reduced  to  powder,  in  order  to  secure  greater  uni- 
formity, and  then  formed  into  bricks  and  burned  in 
the  usual  manner. 

The  furnaces  used  for  burning  cement  are  of  several 
kinds.  The  ordinary  vertical  lime-kiln,  as  mentioned 
in  the  previous  chapter,  is  very  commonly  used,  the 
kiln  being  used  intermittently,  and  requiring  usually 
5  to  10  days  to  burn  a  charge. 

The  Hoffman  continuous  kiln  is  a  series  of  cham- 
bers arranged  in  a  circle,  one  chamber  being  fired  at 
a  time  and  the  products  of  combustion  passing  through 
the  chambers  containing  unburned  material,  the  firing 
progressing  from  chamber  to  chamber  continuously 
around  the  kiln. 

The  Dietzsch  kiln  is  of  the  same  character  as  the 
Hoffman,  but  has  the  fire  outside  the  chamber  contain- 
ing the  material  to  be  burned. 

The  Ransome  kiln  consists  of  a  rotary  cylinder  lined 
with  fire-brick.  The  axis  of  the  cylinder  is  inclined 
at  an  angle  of  10  or  12  degrees  with  the  horizontal, 
and  the  heat  is  applied  as  a  gas-  or  oil-flame  introduced 
through  the  axis  of  the  cylinder  at  its  lower  end.  The 
slurry  is  introduced  in  the  form  of  powder  at  the 
upper  end  of  the  cylinder,  and  is  slowly  carried  to  the 
lower  end  by  the  corrugations  of  the  inner  surface  of 
the  cylinder,  thus  being  gradually  subjected  to  the 
heat,  which  reaches  a  maximum  at  the  lower  end, 


CLASSIFICATION  AND   CONSTITUTION   OF   CEMENT.    2Q 

where  the  clinker  falls  out  either  into  cooling  cylin- 
ders or  upon  floors  from  which  it  is  removed  to 
storage-rooms. 

The  nature  of  the  burning  is  indicated  by  the  color 
of  the  clinker,  which  for  Portland  cement  is  dark  green 
or  black  when  well  burned ;  underburned  material 
being  of  a  lighter  color  and  weight,  while  the  over- 
burned  material  may  powder  upon  cooling,  forming 
what  is  known  as  heavy  powder.  This  heavy  powder 
is  inert  and  does  not  set  as  a  cement,  but  ordinarily 
possesses  puzzolanic  properties  and  becomes  active 
when  mixed  with  lime. 

The  degree  of  burning  required,  as  already  indi- 
cated, varies  with  the  nature  of  the  material  used, 
the  heat  required  being  greater  as  the  hydraulic  index 
of  the  material  becomes  less.  The  heavy  powder 
mentioned  above  is  formed  at  lower  temperatures  as 
the  proportion  of  lime  becomes  less,  and  each  grade 
of  material  has  a  certain  range  of  temperature  within 
which  it  should  be  burned,  below  which  it  will  be 
underburned  and  above  which  it  will  be  rendered 
inert. 

In  underburned  cement  the  chemical  changes  are 
incomplete;  a  part  of  the  lime  may  be  left  as  caustic 
lime  uncombined  with  the  clay.  This  is  shown  by  its 
light  weight.  In  the  burning,  as  the  dehydration  of 
the  materials  and  the  decomposition  of  the  carbonate 
of  lime  is  first  effected,  the  limestone  loses  in  weight 
without  loss  of  volume,  and  thus  suffers  a  loss  in 
apparent  density.  As  the  subsequent  combination  of 
the  lime  with  the  clay  occurs,  a  contraction  in  volume 
takes  place  and  the  density  becomes  greater. 


30  HYDRAULIC   CEMENT, 

After  the  burning  is  completed,  the  clinker  is  broken 
in  a  crusher  to  small  fragments  and  then  ground  to 
powder.  The  cement  is  then  bolted  through  sieves  to 
separate  the  coarse  particles,  which  are  afterward 
returned  to  the  grinders.  The  grinding  is  a  very  im- 
portant matter,  as  only  the  extremely  fine  impalpable 
powder  is  of  real  value  in  the  cement,  and  to  secure 
good  results  the  method  of  grinding  must  be  such  as 
to  produce  a  large  proportion  of  such  material. 

After  the  bolting  of  the  cement  it  is  usually  carried 
to  chambers  and  spread  out  for  aeration,  but  in  some 
cases  is  packed  directly  in  barrels  or  bags  for  shipment. 

The  necessity  for  aeration  depends  upon  the  ac- 
curacy of  the  composition  and  the  completeness  of  the 
chemical  combinations.  Its  object  is  to  eliminate  the 
quicklime  which  may  be  present  by  allowing  it  to 
become  air-slaked. 

The  method  to  be  used  in  manufacturing  cement 
must  in  each  instance  be  modified  to  suit  the  material 
to  be  operated  upon.  The  rock  of  a  single  quarry 
usually  varies  so  much  as  to  require  different  treat- 
ment in  its  various  parts;  or  if  mixtures  are  to  be 
made,  constant  watchfulness  is  required  in  regulating 
the  proportions  in  order  to  obtain  a  product  of  uni- 
form quality. 

ART.  12.     PORTLAND  CEMENT. 

The  term  Portland  Cement  is  usually  limited  to 
material  containing  a  high  percentage  of  lime  and 
burned  at  a  high  temperature.  It  is  usually  low  in 
alumina  and  magnesia.  In  order  to  make  a  good 


CLASSIFICATION  AND   CONSTITUTION  OF  CEMENT.   31 

cement  of  this  character  it  is  necessary  that  the  in- 
gredients be  very  accurately  proportioned  and  that 
the  material  be  very  homogeneous.  This  requires 
ordinarily  the  pulverization  of  the  raw  materials  and 
their  uniform  incorporation  into  the  mixture  in  a  finely 
divided  state. 

The  action  of  Portland  cement  seems  to  depend 
upon  the  formation,  during  the  burning,  of  certain 
silicates  and  aluminates  of  lime  which  constitute  the 
active  elements  of  the  cement,  the  other  ingredients 
being  considered  in  the  light  of  impurities.  The  ideal 
cement  would  be  that  in  which  the  proportion  of  lime 
is  just  sufficient  to  combine  with  all  the  silica  and 
alumina  in  the  formation  of  active  material.  If  there 
be  a  surplus  of  clay  beyond  this  point,  it  forms  inert 
material.  Any  surplus  of  lime  remains  in  the  cement 
as  free  lime,  and  constitutes  one  of  the  chief  dangers 
in  the  use  of  cement,  as,  although  it  may  not  prevent 
the  proper  action  of  the  cement  when  used,  it  may 
cause  the  mortar  to  afterward  swell  and  become 
cracked  and  distorted  as  the  lime  slakes. 

As  perfect  homogeneity  is  not  attainable  in  practice, 
it  is  always  necessary  that  the  clay  be  somewhat  in 
excess  in  order  that  free  lime  be  not  formed.  The 
amount  of  excess  of  clay  necessary  evidently  depends 
upon  the  thoroughness  of  the  process  used  in  manu- 
facture and  the  evenness  which  may  be  reached  in  the 
mixture  of  raw  materials. 

The  hydraulic  index  of  Portland  cement  varies  from 
about  42/100  to  60/100.  The  value  of  the  index  is 
affected  by  the  relative  proportions  of  silica,  alumina, 
and  iron  oxide  contained  by  the  cement  as  the  equiva- 


32  HYDRAULIC  CEMENT. 

lent  weights  of  these  oxides  differ.  The  normal  com- 
position of  Portland  cement  is  usually  within  the  fol- 
lowing limits: 

'    Silica 20      to  25  per  cent. 

Alumina...   5       "         9        " 

Iron  oxide 2       "         5         " 

Lime 57      "  65        " 

Magnesia 0.5    "         2         " 

!  Sulphuric  acid 0.25"         1.50" 

Table  I,  taken  from  Candlot,*  gives  analyses  of  a 
number  of  representative  European  Portland  cements, 
while  Table  II,  collected  from  various  sources,  gives 
analyses  of  a  few  of  the  leading  brands  both  American 
and  foreign  sold  in  this  country. 

A  large  number  of  analyses  of  European  Portland 
cements  are  given  by  Professor  Tetmajerf  which 
show  for  the  most  part  about  the  same  range  of 
variation  as  those  already  given. 

Professor  Le  Chatelier  has  made  a  very  careful  study 
of  the  constitution  of  Portland  cement  by  analyzing 
sections  of  clinker  under  the  microscope,  as  .well  as  by 
studying  synthetically  the  various  compounds  of  the 
principal  ingredients.  He  concludes  $  that  the  tri- 
calcic  silicate,  SiOBCa3 ,  is  the  only  one  that  is  really 
hydraulic  and  is  the  active  element  in  cement.  In 
Portland  cement  he  finds  it  to  be  the  principal  com- 

*  Ciment  et  chaux  hydrauliques  (Paris,  i8gi). 
Method  en    und    Resultate    der    Priifung   der    Hydraulischen 
Bindemittel  (Zurich,  1893). 

J  Annales  des  Mines,  September,  1893. 


CLASSIFICATION  AND   CONSTITUTION  OF  CEMENT.   33 

ponent,  occurring  in  cubical  crystals.  It  is  formed  by 
combination  of  silica  and  lime  in  presence  of  fusible 
compounds  formed  by  the  alumina  and  iron. 

TABLE  I. 

COMPOSITION  OF  PORTLAND  CEMENTS. 


•a 

0 

i 

c* 

'G 

SJ 

I 

2 

<j 

c 

g 

1 

| 

'a 

3 

.ide  of  I 

1 

4 
I 

. 

0 

1 

1 

i/5 

O 

2 

•3 

(75 

1 

f 

22.20 
23.50 

6.72 

7-75 

.28 
•95 

67.31 
64.07 

:3 

26 

60 

0.40 
0.85 

21.70 
23.40 

7.48 

3 

65.54 
63.70 

.90 

-95 

77 

^80 

24.50 

7.09 

.81 

62.40 

•85 

70 

•25 

0.40 

French  cements    • 

25.40 
21.  80 

6.65 
6.56 

'64 

61.60 
57-42 

.08 
•72 

84 

.40 

<x6o 

24-25 

5-20 

•3° 

63.61 

•79 

68 

.40 

0.70 

0.07 

22.30 

8.04 

•7i 

58.68 

.20 

3 

•55 

0.25 

23.00 

8:33 

•87 

60^90 

.10 

.40 

•49 

24.60 

7.98 

•Si 

59.10 

•25 

3-40 

O.II 

23.15 

7.83 

•37 

61.40 

.O? 

47 

1.45 

0.24 

23.30 

7.65 

62.20 

06 

1.60 

0.05 

7.88 

•37 

61.30 

-33 

10 

•95 

.... 

3-7° 

7.80 

•40 

59-36 

•55 

25 

2.25 

8.22 

-38 

60.48 

.00 

35 

•  .00 

0.45 

English  cements  • 

i-95 
i.  60 

7-99 
6.30 

.91 
3° 

59.08 
62.72 

'.98 

52 

•35 
•95 

0.30 

'•35 

7.15 

•75 

62.16 

•95 

06 

0.25 

O-  13 

0.30 

8.63 

•37 

59  92 

.06 

45 

•25 

0.40 

0.62 

3-3° 

8.13 

.67 

60.48 

.60 

20 

.90 

9-73 

97 

59-76 

.60 

68 

O    II 

4-05 
3  50 

8.69 
8-43 

•31 

•47 

59-69 
59-64 

.90 
•97 

% 

:!£ 

'0.60 

.?:?5 

22.60 

7.01 

•04 

63-11 

•79 

37 

.08 

21-75 

8.16 

.64 

63  39 

•3° 

.25 

10.  60 

.60 

62.23 

•44 

68 

.... 

o.  15 

24.85 

6.07 

•43 

64.40 

.26 

5' 

0.48 

German  cements 

22.80 

23.70 

6.30 
5  25 

.70 
.70 

66.40 
67.18 

.08 

63 
40 

0.09 

22.40 

7.30 

.70 

62.83 

.21 

58 

•25 

O.IO 

22.80 

7.46 

.84 

63.28 

•24 

98 

•55 

0.20 

22.25 

7.85 

•3° 

58.12 

.08 

•35 

O.25 

.... 

, 

20.80 

8.66 

.64 

62.52 

.68 

89 

•85 

O.IO 

24.85 

6-45 

7° 

61.44 

.70 

03 

•95 

24.50 

8-5' 

.84 

60.03 

54 

0.60 

Belgian  cements 

24.30 
23-80 

6^39 

•47 
•51 

60.19 
62.32 

.70 
.72 

13 

17 

7° 
94 

1.30 

'o!o8 

26.10 

24.30 

5-79 

.61 

.67 

62.44 

•79 

85 

35 

0.07 

' 

0.17 

34  HYDRAULIC   CEMENT. 

TABLE  II. 

COMPOSITION  OF  PORTLAND  CEMENTS. 


R 

•B 

I 

, 

C 

0 

.2 
£ 

S 

„• 

a 

| 

2 

1 

a 

c 

| 

i 

•o 

i 

< 

0 

J 

* 

1/3 

* 

d 

w 

r 

6.30 

2.50 

66.04 

i.  ii 

0.67 

1-13 

0.28 

German  -1 

22.66 

24-90 

7lf 

2.87 

63  58 

59-98 

1.  10 

o.,8 

0.66 
0.50 

1.26 
2.16 

I 

20.32 

7.86 

3.60 

61.66 

1.85 

1.31 

1.20 

i.o7 

0.80 

English                  ] 

22-45 

23.65 

6.91 
10.56 

3-62 
3-34 

61.04 
60.00 

1.18 
0.97 

1.44 

t.86 

1.50 
0.50 

22.74 

'9-75 

7.48 

44 
5.00 

"ias 

^a 

0.60 

0.97 

0.63 
0.75 

5-40 
2.92 

0.53 

0.65 

American  -j 

20.75 
23.36 
22.45 
20.80 

8'7 

5° 
4.83 
23 
3-70 

62.25 
59.28 
61-37 
62.51 

0.25 

1.  00 

0.66 
1.09 

0.25 
0.50 

1.29 

2.25 
0.50 
0.71 

0.47 
2.46 
0.90 
2.05 

0:;0 

"The  bicalcic  silicate,  SiO4Ca, ,  possesses  the  sin- 
gular property  of  spontaneously  pulverizing  in  the 
furnace  upon  cooling.  This  silicate  does  not  possess 
hydraulic  properties  and  will  not  harden  under  water, 
but  it  is  rapidly  attacked  by  carbonic  acid,  forming 
carbonate  of  lime,  and  thus  contributes  something  to 
the  final  hardening  of  mortar  employed  in  air.  The 
admixture  of  magnesia  to  form  the  double  silicate  of 
lime  and  magnesia,  SiO4MgCa,  prevents  the  pulver- 
ization. This  silicate  is  of  no  value  for  cement. 

"  At  a  very  high  heat  the  tricalcic  silicate  is  decom- 
posed into  the  bicalcic  silicate  and  free  lime,  thus 
becoming  inert." 

"  There  are  various  aluminates  of  lime,  all  of  which 
set  rapidly  in  contact  with  water.  The  most  impor- 
tant is  the  tricalcic  aluminate,  Al2O6Caa. 

"  With  Portland  cement  a  fusible  silico-aluminate 


CLASSIFICATION   AND   CONSTITUTION  OF  CEMENT.    35 

of  lime,  2SiO.,,Al.2O3,3CaO,  is  formed,  identical  with 
that  which  forms  the  essential  element  of  blast-furnace 
slag,  with  a  portion  of  iron  replacing  alumina.  This 
compound  is  inert  under  the  action  of  water  and  does 
not  seem  to  be  attacked  by  carbonic  acid.  Its  useful 
function  is  to  assist  the  combination  of  silica  with  the 
lime. 

"  This  silico-aluminate,  which  is  crystallized  in 
Portland  cement  on  account  of  slow  cooling,  is  in  a 
vitreous  condition  when  the  cooling  is  sufficiently 
brisk,  as  in  the  case  of  blast-furnace  slag  precipitated 
into  cold  water.  It  combines  with  hydrate  of  lime  in 
setting,  and  gives  rise  to  the  hydrated  silicates  and 
aluminate  of  lime  identical  with  those  formed  during 
the  setting  of  Portland  cement.  It  is  these  properties 
upon  which  are  based  the  manufacture  of  slag-cement. 

Prof.  Le  Chatelier  gives  two  limits  within  which  the 
quantity  of  lime  in  Portland  cement  should  always  be 
found.  These  are,  that  the  proportion  of  lime  should 
always  be  greater  than  that  represented  by  the  formula 

CaO+MgO 


Si03  -  ALA  - 

and  that  it  should  never  exceed  that   given  by  the 
formula 

CaO  +  MgO 

~3' 


The  symbols  in  these  formulas  represent  the  number 
of  equivalents  of  the  substances  present,  not  the 
weights.  One  third  the  number  of  equivalents  of  sul- 


36  HYDRAULIC   CEMENT. 

phuric  acid  should  be  added  to  the  denominator  in 
each  case. 

This  is  based  upon  the  theory  that  the  essential  in- 
gredients of  the  cement  are  the  tricalcic  silicate  and 
aluminate  of  lime  and  the  silico-aluminate  already  men- 
tioned. Formula  (i)  represents  the  point  at  which 
the  amount  of  lime  present  would  be  just  sufficient  to 
form  the  tricalcic  silicate  and  the  silico-aluminate,  no 
tricalcic  aluminate  being  formed.  If  less  lime  than 
this  be  present,  the  bicalcic  silicate  would  be  formed. 

Formula  (2)  represents  the  point  at  which  the 
amount  of  lime  would  be  sufficient  to  form  the  tricalcic 
silicate  and  aluminate  to  the  exclusion  of  the  silico- 
aluminate.  If  more  lime  than  this  be  present,  it  will 
remain  in  the  form  of  free  lime. 

It  is  also  stated  by  Prof.  Le  Chatelier  that  for  Port- 
land cement  of  good  quality  formula  (i)  usually  gives 
3.5  to  4,  and  formula  (2)  gives  2.5  to  2.7  as  a  result. 

An  examination  of  the  analyses  of  a  considerable 
number  of  samples  of  good  Portland  cement  shows 
that  in  nearly  all  cases  the  requirements  of  the  formulas 
are  met,  and  that  most  of  them  give  results  within  the 
limits  specified  above,  but  there  are  good  cements  for 
which  formula  (i)  gives  considerably  higher  results 
than  4. 

Dr.  Erdmenger  considers  *  that  the  equations  are 
not  borne  out  by  experience,  as  they  involve  the 
assumption  that  rhagnesia  may  be  considered  as  lime. 
It  is  also  pointed  out  that  the  formation  of  the  bicalcic 
silicate  depends  upon  the  temperature  of  burning,  and, 

*  Journal  Society  of  Chemical  Industry,  xi.  1035. 


CLASSIFICATION   AND   CONSTITUTION   OF   CEMENT.   37 

according  to  Prof.  Le  Chatelier,  the  tricalcic  silicate 
may  be  decomposed,  and  become  inert  at  a  sufficient 
temperature. 

Dr.  Erdmenger  also  states  that  the  powdering  upon 
cooling  may  in  some  instances  be  prevented  by  cool- 
ing suddenly,  as  by  plunging  into  cold  water,  and  that 
when  so  treated  the  material  does  not  become  inert. 

When  cement  is  burned  in  contact  with  the  fuel, 
the  composition  is  modified  by  the  combination  of  the 
silica  of  the  fuel  with  the  lime.  According  to 
M.  Bonnami  a  sort  of  grappiers  is  thus  formed,  as 
with  hydraulic  lime,  particles  being  thus  produced  less 
basic  than  the  rest  of  the  cement,  and  of  the  charac- 
ter of  puzzolana.  This  material  is  distributed  through 
the  cement  in  grinding  and  tends  to  slightly  raise  the 
hydraulic  index.  It  is  inert  of  itself,  but  may  act  like 
a  puzzolana  in  combining  with  lime  in  the  final  harden- 
ing of  the  cement. 

Portland  cement  when  of  low  index  and  thoroughly 
burned  usually  sets  slowly,  but  varies  greatly  in  this 
respect,  as  the  composition  changes  or  the  degree  of 
burning  is  modified.  It  commonly  gains  its  ultimate 
strength  much  more  rapidly  than  natural  cements. 


ART.  13.     NATURAL  CEMENTS. 

The  term  Natural  Cement  is  commonly  employed 
to  designate  a  large  number  of  widely  varying  products 
formed  by  burning  natural  rock  without  pulverization 
or  the  admixture  of  other  materials.  These  cements 
are  usually  of  higher  hydraulic  index  than  the  Port- 

182O27 


38  HYDRAULIC   CEMENT. 

lands,  and  consequently  more  lightly  burned.  The 
index  varies  from  about  60/100  to  150/100. 

The  quick-setting  natural  cements,  or  Roman  Cem- 
ents as  they  are  called  in  Europe,  are  obtained  by 
burning,  at  a  comparatively  low  temperature,  argil- 
laceous limestones  of  rather  high  index.  These 
cements  are  usually  characterized  by  a  very  rapid  set, 
and  slowness  in  gaining  strength  subsequently.  The 
feeble  burning  gives  incomplete  reactions,  and  the 
formation  of  the  silicates  of  lime  is  not  so  complete  as 
in  the  heavily  burned  Portland  cements.  A  consider- 
able percentage  of  aluminate  of  lime  is  present,  which 
is  the  cause  of  the  quick  set,  and  there  is  usually  a 
strong  proportion  of  sulphate  of  lime,  which  is  regarded 
as  a  necessary  ingredient  having  the  tendency  to  make 
the  set  more  slow,  where  it  might  otherwise  be  too 
rapid  for  practical  use.  Some  unburned  material  is 
also  commonly  present  in  such  cements,  remaining  as 
inert  matter.  Material  of  this  character  becomes  inert 
when  the  temperature  of  burning  is  increased  to  the 
point  where  the  chemical  reactions  would  become 
complete,  the  heavy  powder  previously  mentioned 
being  formed  at  a  much  lower  temperature  than  in 
cement  containing  a  higher  percentage  of  lime. 

Table  III  gives  results  of  analyses  of  a  number  of 
the  leading  European  Roman  cements  collected  from 
various  sources,  and  showing  the  ordinary  range  of 
variation  in  composition  for  good  material. 

The  semi-slow-setting  natural  cements  of  Europe 
are  often  known  as  Natural  Portland  Cements.  These 
are  often  of  a  composition  quite  similar  to  Portland 
cement,  but  usually  have  a  higher  hydraulic  index  and  . 


CLASSIFICATION   AND   CONSTITUTION   OF  CEMENT.    39 


TABLE  III. 

COMPOSITION  OF   EUROPEAN   ROMAN  CEMENTS. 


1 

0 

J) 

3 
t/5 

Alumina. 

Iron  Oxide. 

§ 

j 

A 

i 

1 

Sulphuric  Acid. 

Loss  on  Ignition. 

Not  Determined. 

, 

22.60 

8.90 

5-30 

52.69 

1-15 

3-25 

6.  1  1 

2 

6  oo 

24.80 

7.00 

4.8o 

44.12 

2.08 

3.60 

7.50 

0.  IO 

3 

21.70 

8.29 

3-71 

52.68 

3-52 

3.56 

6.  20 

0-34 

4 

23.60 

7-99 

4.31 

5740 

1.50 

2.IO 

2-75 

o-35 

5 

21.80 

10.03 

3-77 

55.00 

2.80 

2.74 

3-75 

O.I  I 

6 

2.00 

26.80 

10.39 

4.61 

46.10 

1.72 

i-74 

6.40 

0.24 

7 

10.70 

30  80 

7.82 

5-'3 

33-04 

0.93 

2.90 

8.20 

0.48 

8 

2.40 

25-45 

9.25 

3-85 

47-95 

I  45 

0.70 

8.95 

.... 

9 

29-55 

8-35 

4.10 

47-50 

3-85 

i-35 

5.30 

10 

.... 

21.00 

8.40 

5-10 

52.05 

1   OO 

2   5O 

9-95 

ii 

.... 

23.40 

12.90 

3-30 

47.70 

1.05 

3-30 

8-35 

12 

0.85 

29.05 

7-95 

3-75 

46.05 

2.80 

I.IO 

8-45 

.... 

J3 

.... 

25.85 

9.10 

4.10 

51.60 

0.85 

1.50 

7-00 

.... 

M 

4.35 

27-35 

7-73 

3-85 

50.25 

1-05 

0-55 

4-85 

>  •  •• 

15 

25-85 

IO.OO 

4-85 

54-20 

1.65 

1.  00 

2-45 

.... 

16 

29.10 

12.50 

4.65 

48.60 

1.70 

1.90 

i-55 



17 

3.40 

24  65 

"•35 

5-25 

50.45 

1-15 

1-25 

2.50 

.... 

18 

0.50 

20.00 

8.40 

5-70 

52.05 

c-95 

2.80 

9.60 

.... 

19 

2.60 

27.10 

4.10 

3-75 

48.70 

0.65 

0.95 

12.15 

.... 

20 

.... 

28.06 

6.65 

3-30 

47-79 

i.  08 

1.66 

10.44 

21 

.... 

27-54 

9-25 

3-8o 

54.58 

0.50 

0.64 

3.69 



22 

20.54 

8.72 

3-23 

5I-85 

2.31 

3-93 

9.28 

.... 

23 

.... 

21.04 

12.72 

4.04 

5I-38 

1.20 

5-5i 

3-65 

24 

21.29 

9-36 

3-5i 

5«-74 

4.24 

6.01 

3-22 

.... 

25 

23  35 

9.69 

2.96 

54-71 

i.oS 

1.95 

4-31 

.... 

26 

20.60 

9.92 

2.56 

52.42 

3-91 

6.06 

3-30 

.... 

27 

28.36 

12.12 

1-57 

47.28 

2.24 

2.OO 

4-52 

.... 

28 

.... 

25.64 

8.76 

2.15 

44-87 

1-93 

5-U 

10.  16 

.... 

29 

25.70 

9.26 

3-38 

50.86 

1-54 

1.51 

6.67 

.... 

30 

.... 

29.74 

11.92 

3-68 

42.98 

2.0S 

2.34 

6.20 

.... 

31 

.... 

22.14 

8.74 

3-69 

58.41 

2.  02 

2.90 

2.12 

32 

— 

23-35 

8.20 

3-74 

57-94 

1.63 

2.98 

2.S2 



are  given  a  somewhat  lighter  burning.  They  are, 
however,  more  heavily  burned  than  the  Roman  cem- 
ents. Limestones  in  nature  are  not  so  homogeneous 
as  the  artificial  mixtures  used  in  making  Portland 


4O  HYDRAULIC   CEMENT. 

cement,  and  the  proportion  of  lime  cannot  be  so  great 
as  in  the  more  homogeneous  mixtures  without  danger 
of  producing  an  objectionable  quantity  of  free  lime  in 
the  cement.  The  use  of  material  of  this  character, 
therefore,  requires  much  care  in  order  to  produce  good 
results.  As  the  hydraulic  index  becomes  greater  the 
homogeneity  becomes  less  important,  as  free  lime 
becomes  less  likely  to  occur  and  less  dangerous,  and 
irregularities  only  have  the  effect  of  increasing  the 
quantity  of  inert  matter,  which  causes  mortar  made 
from  the  cement  to  gain  strength  much  more  slowly 
than  with  Portland  cement  of  low  index.  It  is  to  be 
observed  that  the  material  spoken  of  as  inert,  and 
which  delays  the  gain  in  strength  in  the  early  period 
of  hardening,  may  not  be  altogether  inert,  and  may 
contribute  to  the  final  strength  of  the  cement,  as  it  is 
of  a  puzzolanic  character  and  perhaps  ultimately  com- 
bines with  the  hydrated  lime  in  the  mortar. 

These  cements  occupy  an  intermediate  position 
between  the  artificial  Portland  cements  and  the  Roman 
cements,  and  may  approach  either  in  composition.  In 
fact,  the  same  raw  material  may  frequently  produce 
either — if  burned  lightly  giving  the  quick-setting 
Roman  cement,  or  burned  more  heavily  a  slow-setting 
natural  Portland.  Heavy  burning  increases  the  amount 
of  silica  combined  with  lime  at  the  expense  of  the 
aluminates,  thus  relaxing  the  rapidity  of  set  and  in- 
creasing the  early  strength  of  the  mortar. 

The  Llagnesian  Natural  Cements  are  those  in  which 
a  portion  of  the  lime  of  the  Roman  cement  is  replaced 
by  magnesia.  Very  little  is  known  as  to  the  action  of 
the  magnesia  in  these  cements.  It  seems  probable 


CLASSIFICATION   AND   CONSTITUTION   OF   CEMENT.   41 

that  the  magnesia  replaces  lime  or  combines  with  it 
in  the  formation  of  double  silicates  and  aluminates, 
and  that  it  bears  some  part  in  the  setting  and  harden- 
ing of  the  mortar.  That  certain  magnesian  salts 
possess  hydraulic  properties  is  well  known,  their  action 
according  to  M.  Fremy  being  probably  much  slower 
than  the  corresponding  lime-salts. 

The  action  of  cements  of  this  class  is  somewhat 
similar  to  that  of  Roman  cements:  they  gain  strength 
very  slowly,  but  may  be  either  quick  or  slow  setting. 
The  composition  of  the  magnesian  cements  varies  from 
that  of  the  Roman  cements  to  one  in  which  the  pro- 
portion of  magnesia  is  as  large  as  that  of  lime.  As 
the  proportion  of  magnesia  to  lime  increases,  the 
hydraulic  index,  considering  magnesia  as  lime,  fre- 
quently decreases  and  becomes  less  than  would  be 
admissible  in  Roman  cement. 

Magnesian  cements  are  but  little  used  in  Europe, 
but  in  the  United  States  they  form  the  largest  part  of 
the  natural  cements  in  use,  and  many  of  them  have 
been  found  by  experience  to  be  very  useful  and  reli- 
able materials.  The  Rosendale  cements  are  of  this 
character.  The  rock  from  which  these  cements  are 
made  differs  greatly  in  character  in  the  same  locality, 
and  in  the  different  strata  of  the  same  quarry.  In 
some  of  the  works  the  nature  of  the  product  is  regu- 
lated by  mixing  in  proper  proportions  the  clinker 
obtained  by  burning  the  rock  from  different  strata. 
Each  portion  of  rock  must  be  burned  in  such  degree 
as  is  suited  to  its  composition,  and  hence  as  the  ma- 
terial is  not  pulverized  before  burning  it  must  be 
burned  separately  and  mixed  afterward.  To  produce 


42  HYDRAULIC   CEMENT. 

uniformly  good  cement,  therefore,  requires  close  and 
careful  attention;  and  for  this  reason  there  is  often 
considerable  difference  in  the  quality  of  cement  made 
by  works  in  the  same  locality  and  from  very  similar 
material. 

Cement  of  high  index,  unlike  Portland  cement,  is 
usually  materially  changed  by  age.  When  these 
cements  are  kept  exposed  to  the  air  for  a  considerable 
length  of  time,  they  gradually  become  slower-setting 
and  perhaps  eventually  lose  the  power  of  setting 
altogether",  sometimes  becoming  puzzolana,  which 
again  becomes  active  cement  by  reburning. 


ART.  14.     SLAG-CEMENTS. 

Slag-cement  is  formed  by  the  admixture  of  slaked 
lime  with  ground  blast-furnace  slag.  The  slag  has 
approximately  the  composition  of  an  hydraulic  cement, 
but  lacks  a  proper  proportion  of  lime  to  render  it 
active  as  a  cement.  These  cements  are  sometimes 
called  puzzolana  cements,  the  slag  used  being  of  the 
same  nature  as  the  puzzolana  commonly  employed  in 
making  lime  hydraulic. 

The  method  employed  in  forming  slag-cement  is  to 
cool  the  slag  suddenly  by  plunging  it  into  a  current  of 
water  as  it  emerges  from  the  furnace.  This  makes  the 
slag  granular,  and  causes  it  to  retain  the  heat  of  crys- 
tallization, thus  rendering  its  elements  more  ready  to 
enter  into  combination  in  presence  of  water. 

Experience  in  Europe  shows  that  the  slag  must  be 
basic  in  order  to  be  of  use  in  making  cement.  Pro- 


CLASSIFICATION   AND   CONSTITUTION   OF   CEMENT.   43 
fessor  Tetmajer*  arrives  at  the  conclusion  that  slags  in 

which  the  ratio  -TTT  —  is  unity  are  not  suitable,  and  that 
silica 

above  this  proportion  the  value  of  the  product  in- 
creases with  this  ratio.  He  also  finds  that  the  best 
results  are  obtained  from  slags  giving  a  ratio 

Al,03 

T-3  =  45/100  to  50/100. 


M.  Prost  f  states  that  a  considerable  amount  of 
sulphur  may  be  unobjectionable  in  slag-cements,  and 
mentions  a  case  where  good  results  had  been  obtained 
with  sulphurous  slag,  the  only  effect  being  discolora- 
tion attributed  to  sulphide  of  iron.  He  also  concludes 
that  a  slag  is  most  advantageous  for  this  purpose  which 
is  most  rich  in  lime  and  alumina. 

It  is  very  important  in  slag-cements  that  the  slag  be 
ground  very  fine,  and  be  very  intimately  mixed  with 
the  lime.  The  lime  is  slaked  and  bolted,  arid  then 
ground  mechanically  with  the  slag  powder  so  as  to 
insure  thorough  incorporation  into  the  mixture. 

In  consequence  of  the  necessity  of  attaining  extreme 
pulverization  of  the  slag,  it  is  necessary  to  first  dry  it. 
The  water  which  serves  to  make  it  granular  remains 
to  some  extent  between  the  grains  and  makes  bad 
lumps  at  time  of  grinding.  It  has  been  attempted  to 
substitute  quicklime  for  slaked  lime  and  use  this  water 
for  slaking,  but  unsuccessfully,  the  slag  combining  to 
some  extent  with  the  lime  and  thus  weakening  the 

*  Annales  de  les  Construction,  Juillet*  1886. 
f  Annales  des  Mines,  1889.  vol.  II.  p.  158. 


44  HYDRAULIC   CEMENT. 

cement,  while  particles  of  quicklime  being  left  in  the 
cement  cause  swelling  of  the  mortar  after  setting. 
The  drying  is  done  in  a  furnace  at  a  dull  red  heat. 

The  powdered  slag  is  bolted  through  a  fine  sieve — 
about  10,000  meshes  per  square  inch — before  mixing 
with  the  lime. 

The  lime  may  advantageously  be.  kept  for  some 
time  after  slaking  before  being  used,  as  this  insures 
the  complete  reduction  of  the  quicklime,  but  the  slag 
seems  to  deteriorate  when  kept  long  after  grinding. 
Fat  lime  is  commonly  employed  for  this  purpose,  but 
there  seems  to  be  an  advantage  in  using  meagre  lime 
on  account  of  the  mortar  being  less  likely  to  crack 
when  used  in  the  air.  M.  Prost  found  that  there  was 
no  advantage  to  the  strength  of  the  cement  in  using 
hydraulic  lime.  Various  additions  of  puzzolanic  or 
other  material  are  also  sometimes  resorted  to  for  the 
purpose  of  preventing  the  cracking  in  air  when  fat  lime 
is  used..  This  also  increases  the  activity  of  the 
cement. 

The  composition  of  slag-cement  usually  differs  from 
that  of  Portland  in  having  a  less  quantity  of  lime,  more 
silica  and  alumina,  and  more  alumina  in  proportion  to 
the  silica. 

Table  IV  gives  the  composition  of  a  number  of 
samples  of  the  leading  European  slag-cements,  taken 
from  Candlot  and  Tetmajer. 

Slag-cement  is  usually  slow-setting,  but  the  activity 
varies  greatly  with  the  circumstances  of  use.  The 
rapidity  of  action  is  greater  as  the  proportions  of  lime 
and  alumina  increase. 

Slag-cement  acts  better  under  water  than  in  the  air. 


CLASSIFICATION  AND  CONSTITUTION  OF  CEMENT.  4$ 


TABLE  IV. 

COMPOSITION  OF  SLAG-CEMENTS. 


Silica. 

Alumina. 

Iron 
Oxide. 

Lime. 

Mag- 
nesia. 

Sul- 
phuric 
Acid. 

Loss 
on 
Ignition. 

Not 
Deter- 
mined. 

I 

24.80 

I9-I3 

2.67 

36.60 

6.76 

.IO 

7-50 

0-44 

2 

24.60 

13.46 

0.84 

5O.22 

2.65 

•70. 

5-40 

0.13 

3 

24.90 

I3-46 

2.83 

50.40 

I.  2O 

.IO 

6-45 

4 

24.30 

13-85 

I-I5 

49  50 

2.16 

.86 

6.90 

O.28 

5 

27-45 

14.65 

r  -75 

46.20 

1.86 

•72 

7.00 

o-37 

6 

25.20 

15.23 

0.77 

50.00 

1-35 

.72 

6.50 

0.23 

7 

20.40 

18.59 

o  41 

50.07 

0.50 

.08 

8.30 

8 

18.30 

18.07 

0-34 

53-16 

0.64 

.  18 

8.07 

9 

22.35 

12.83 

0.64 

55.61 

2.17 

•27 

4.01 

10 

27-35 

9-13 

1.50 

50.28 

5.72 

.40 

2.59 

ii 

20.35 

14-05 

o.3J 

50.26 

2.68 

•39 

6.99 

12 

18.69 

9.20 

2.14 

46-36 

4.92 

-25 

12.19 

13 

19.87 

14.84 

0.80 

48.54 

2-44 

.00 

8.41 

M 

i8.ii 

15-54 

0.92 

54-72 

0-54 

•  37 

8.64 

15 

20.94 

14-85 

1.03 

48.18 

3.58 

.69 

7.22 

16 

19.24 

I7.I5 

1.07 

54-21 

0.81 

•39 

6-39 

It  is  essentially  a  hydraulic  material,  and  it  is  especially 
important  that  it  be  kept  damp  during  the  early  period 
of  hardening,  in  order  that  the  water  necessary  to  its 
proper  hardening  may  not  evaporate. 

M.  Frost  states  that  slag-cement  is  sensitive  to  the 
action  of  frost,  and  should  not  be  used  in  freezing 
weather;  while  Mr.  Redgrave  declares  that  it  resists 
frost  better  than  Portland — showing  a  difference  of 
experience  in  France  and  England. 

Mr.  Redgrave  also  says  that  it  may  be  kept  a  long 
time  without  injury,  and  if  kept  free  from  moisture' 
that  it  undergoes  no  change  whatever;  while  M.  Bon- 
naini  states  that  exposed  to  air  in  powder  it  rapidly 
loses  its  hydraulic  properties,  probably  through  car- 
bonization. 


46  HYDRAULIC   CEMENT. 


ART.  15.     MIXED  CEMENTS. 

The  term  Mixed  Cement  is  sometimes  used  to  in- 
clude a  considerable  number  of  cements  which  are 
formed  by  a  mixture  of  various  products  occurring  at 
works  where -other  cement  is  made.  These  mixtures 
may  be  made  either  for  the  purpose  of  cheapening  the 
product  or  of  imparting  to  it  certain  desired  qualities. 
They  consist  of  admixtures  of  different  grades  of 
cement,  of  the  overburned  or  underburned  portions  of 
clinker,  or  of  foreign  material  added  to  the  cement. 

Slag-cements  and  certain  natural  cements  which, 
like  some  of  the  Rosendales,  are  made  by  mixing 
different  grades  of  clinker  are  sometimes  included 
under  this  head,  but  are  not  what  is  usually  meant  by 
the  term. 

Mixed  cements  differ  so  widely  in  character  that  no 
general  discussion  of  their  attributes  is  possible.  Their 
values  depend  upon  the  care  used  in  selecting,  pro- 
portioning, and  incorporating  the  ingredients,  and  each 
works  has  its  own  method  of  manufacture.  In  some 
cases,  light-burned  Roman  cement  is  made  slow-set- 
ting by  the  admixture  of  grappiers  obtained  in  the 
slaking  of  hydraulic  lime,  with  sometimes  an  addition 
of  Portland  cement.  The  overburned  clinker  from 
the  manufacture  of  Portland  cement  is  also  sometimes 
utilized  by  being  mixed  with  natural  cement,  a  cer- 
tain amount  of  Portland  cement  being  added  to  bring 
up  the  initial  strength  and  reduce  the  rapidity  of  set. 

Cement  of.  this  kind  is  usually  sold  under  the  desig- 
nation of  Portland  or  natural  cement,  and  not  accord- 


CLASSIFICATION   AND   CONSTITUTION  OF  CEMENT.   47 

ing  to  its  real  character.      Some  of  them  when  carefully 
and  regularly  made  give  good  results  in  practice. 


ART.  16.     GRAPPIERS  CEMENT. 

Grappiers  cements  are  made  by  grinding  to  powder 
the  grappiers  left  from  the  slaking  and  bolting  of 
hydraulic  lime.  Very  great  care  is  necessary  in  elimi- 
nating all  of  the  free  lime  from  the  grappiers  by 
thorough  slaking,  the  operation  of  slaking  and  bolting 
being  repeated  several  times.  The  grappiers  includes 
the  underburned  stone,  and  overburned  material 
formed  in  contact  with  the  fuel,  as  well  as  a  certain 
amount  of  hard-burned  material  of  too  high  hydraulic 
index  to  slake,  and  similar  in  composition  and  action 
to  Portland  cement.  This  latter  is  the  effective  por- 
tion of  the  cement,  and  it  predominates  in  grappiers 
of  good  quality. 

These  cements  are  usually  of  low  index  and  very 
slow-setting.  They  are  liable  to  contain  free  lime 
unless  carefully  handled  and  usually  require  exposure 
to  the  air  after  grinding  to  permit  them  to  become 
air-slaked. 

At  Teil  the  grappiers  are  passed  through  coarse 
grinders,  which  serve  to  remove  all  the  soft  parts.  It 
is  then  bolted,  allowed  to  air-slake  for  a  month,  then 
bolted  again.  Finally  the  parts  resisting  slaking  are 
ground,  steam  being  present  to  slake  the  particles  of 
free  lime,  after  which  it  is  air-slaked  before  packing 
for  shipment 


48  HYDRAULIC   CEMENT. 


ART.  17.     SAND-CEMENT. 

Sand-cement  is  the  name  given  to  material  formed 
by  grinding  together  Portland  cement  ana  sand  to  an 
extremely  fine  powder  and  a  very  intimate  mixture. 
It  is  claimed  that  a  very  considerable  amount  of  sand 
may  thus  be  mixed  with  the  cement  without  materially 
reducing  its  strength,  and  that  the  sand-cement  so 
made  may  still  be  mixed  with  the  usual  proportions 
of  ordinary  sand  and  give  good  results  in  use. 

It  is  said  that  the  additional  grinding  given  the 
cement  in  pulverizing  the  sand  reduces  the  cement  to 
impalpable  powder,  thus  increasing  its  power  of  "  tak- 
ing sand."  Experiments  also  seem  to  indicate  that 
if  sand  be  powdered  separately,  a  certain  amount  may 
be  mixed  with  cement  without  serious  injury  to  mor- 
tar made  from  the  cement. 


CHAPTER   III. 
THE  SETTING  AND   HARDENING  OF  CEMENT. 

ART.  18.     THE  SETTING  OF  CEMENT. 

WHEN  cement-powder  is  mixed  with  water  to  a 
plastic  condition  and  allowed  to  stand,  it  gradually 
combines  into  a  solid  mass,  taking  the  water  into 
combination,  and  soon  becomes  firm  and  hard.  This 
process  of  combination  amongst  the  particles  of  the 
cement  is  known  as  the  setting  of  the  cement. 

Cements  of  different  character  differ  very  widely  in 
their  rate  and  manner  of  setting.  Some  occupy  but 
a  few  minutes  in  the  operation,  while  others  require 
several  hours.  Some  begin  setting  immediately  and 
take  considerable  time  to  complete  the  set,  while 
others  stand  for  a  considerable  time  with  no  apparent 
action  and  then  set  very  quickly. 

The  points  where  the  set  is  said  to  begin  and  end 
are  necessarily  arbitrarily  fixed,  and  are  differently 
determined — usually  by  trying  when  the  mortar  will 
sustain  a  needle  carrying  a  specified  weight.  The 
beginning  of  set  is  usually  supposed  to  be  when  the 
stiffening  of  the  mass  first  becomes  perceptible,  and 
the  end  of  set  is  when  the  cohesion  extends  through 
the  mass  sufficiently  to  offer  such  resistance  to  any 

49 


50  HYDRAULIC   CEMENT. 

change  of  form  as  to  cause  rupture  before  any  per- 
ceptible deformation  can  take  place. 

It  is  sometimes  stated  that  the  chemical  change  in- 
volved in  setting  is  an  instantaneous  occurrence  at 
about  the  time  we  call  the  beginning  of  set,  and  that 
the  gradual  hardening  then  begins  and  is  a  continuous 
process  until  the  maximum  strength  is  reached.  How- 
ever this  may  be,  with  some  cements  a  quite  notice- 
able change  suddenly  shows  itself  at  about  this  time  in 
the  disappearance  of  water  from  the  surface  of  the 
mortar  and  the  sudden  stiffening  of  the  mass. 

ART.  19.    THE  HARDENING  OF  CEMENT  MORTAR. 

After  the  completion  of  the  setting  of  the  cement 
the  mortar  continues  to  increase  in  cohesive  strength 
over  a  considerable  period  of  time,  and  this  subsequent 
development  of  strength  is  called  the  hardening  of  the 
cement. 

The  process  of  hardening  appears  to  be  quite  dis- 
tinct from,  and  independent  of,  that  of  setting.  A 
slow-setting  cement  is  apt,  after  the  first  day  or  two, 
to  gain  strength  more  rapidly  than  a  quick-setting 
one;  but  it  does  not  necessarily  do  so.  The  ultimate 
strength  of  the  cement  is  also  quite  independent  of  the 
rate  of  setting.  A  cement  imperfectly  burned  may 
set  more  quickly  and  gain  less  ultimate  strength  than 
the  same  cement  properly  burned,  but  of  two  cements 
of  different  composition  the  quicker-setting  may  be 
the  stronger. 

There  is  as  wide  variation  in  the  rate  of  hardening 
of  different  cements  as  in  the  rate  of  setting:  some 


THE   SETTING   AND   HARDENING   OF  CEMENT.       51 

gain  strength  rapidly  and  attain  their  ultimate  strength 
in  a  few  days,  while  others  harden  more  slowly  at  first 
and  continue  to  gain  in  strength  for  several  years. 
The  rate  of  early  hardening  gives  but  little  indication 
of  the  ultimate  action  of  the  cement,  as  the  final 
strength  of  the  mortar  may  be  the  same,  however 
rapidly  the  strength  is  attained. 

Portland  cement  usually  hardens  more  rapidly  and 
gains  its  maximum  strength  more  quickly  than  natural 
cement,  and  also,  as  a  rule,  the  Portland  cement 
attains  greater  final  strength  when  used  in  the  same 
manner.  Of  two  cements  of  the  same  class,  however, 
it  is  not  safe  to  infer  that  that  which  most  rapidly 
gains  strength  will  prove  the  stronger  and  more  per- 
manent material ;  in  fact,  where  an  abnormally  high 
strength  is  shown  in  a  few  days  the  presumption  as  to 
final  strength  is  against  the  cement  giving  such  result, 
and  in  favor  of  one  hardening  at  a  more  moderate  rate. 

The  rate  at  which  cement  should  harden  for  a  given 
use  depends,  of  course,  upon  the  necessity  of  devel- 
oping early  strength  in  the  work.  For  many  pur- 
poses, such  as  most  subaqueous  construction,  high 
early  strength  is  quite  desirable  if  not  necessary ;  but 
for  most  engineering  work  a  very  rapid  hardening  does 
not  seem  necessary,  and  better  results  may  often  be 
obtained  by  the  use  of  a  material  of  more  gradual 
action. 

ART.  20.     CHEMICAL  THEORY. 

Very  little  is  definitely  known  concerning  the  chem- 
ical reactions  which  take  place  in  the  process  of  setting 


52  HYDRAULIC   CEMENT. 

and  hardening  of  cement-mortars.  Many  theories 
have  been  proposed  to  account  for  the  phenomena  by 
different  observers,  based  mainly  upon  the  study  of 
the  properties  of  various  compounds  of  lime,  silica, 
and  alumina  formed  synthetically.  Chemical  analysis 
shows  the  proportions  of  the  various  elementary  sub- 
stances of  which  the  cement  is  composed,  but  not 
their  state  of  combination  ;  and  the  action  of  a  cement 
may  be  greatly  modified  by  altering  the  condition  in 
which  the  ingredients  exist,  through  changing  the 
manipulation  in  manufacture,  without  altering  their 
relative  quantities. 

M.  Fremy  considered  Portland  cement  to  be  very 
complex  in  composition,  and  ascribed  the  setting  to 
the  action  of  lime  upon  certain  puzzolanic  compounds, 
composed  of  double  silicates  of  lime  and  alumina,  the 
calcination  of  the  clay  giving  rise  to  a  porous  material 
which  absorbs  the  lime  by  capillary  affinity. 

M.  Landrin  concluded  that  a  substance  correspond- 
ing to  the  formula  3SiO2,5CaO  is  found  in  both  Port- 
land cements  and  puzzolana,  and  he  considered  this  to 
be  the  active  element  in  the  hardening  of  cement, 
although  he  states  that  aluminate  of  lime  contributes 
to  the  setting  and  accelerates  that  action. 

Prof.  Le  Chatelier,  from  his  study  of  Portland 
cements,  explains  the  phenomena  of  setting  by  show- 
ing that  certain  salts,  including  the  aluminate  and 
silicate  of  lime  which  form  the  active  elements  of 
Portland  cement,  while  soluble  in  an  anhydrous  state, 
form  insoluble  salts  when  hydrated.  When  they  come 
into  contact  with  water  in  mixing  mortar  the  anhy- 
drous sale  enters  into  solution,  then,  becoming  hy- 


THE  SETTING  AND   HARDENING   OF  CEMENT.        53 

drated,  the  hydrate  is  precipitated  from  the  saturated 
solution  in  a  crystalline  form.  Those  salts  which  are 
thus  capable  of  being  dissolved  in  an  anhydrous  state 
and  then  becoming  hydrated  arrive  at  stability  in  two 
ways — by  decomposition  and  by  combination. 

The  tricalcic  silicate,  which  is  the  essential  element 
of  Portland  cement,  is  decomposed  in  presence  of 
water  to  a  hydrated  monocalcic  silicate  and  a  hydrate; 
thus 

Si06Ca2  +  Aq  =  SiO,,CaO,2.5H,O  +  2CaO,H,O. 

The  monocalcic  silicate  crystallizes  in  the  form  of 
needle-like  crystals  and  the  hydrate  in  hexagonal 
lamina  visible  to  the  eye.  The  tricalcic  aluminate  is 
hydrated  by  simple  combination  with  the  water. 

Al2O6Ca3  -f  Aq  =  AlaO3.3CaO,  I2H2O. 

The  double  silicate  of  alumina  and  iron,  2SiO.,, 
AlaOs,3CaO,  is  thought  to  be  quite  inert  in  Portland 
cement,  and  to  merely  serve  the  purpose  of  assisting 
the  combination  of  the  silica  and  lime  by  acting  as  a 
flux  during  burning.  It  seems,  however,  to  be  an 
active  element  in  slag-cement,  forming  by  combina- 
tion with  lime  in  presence  of  water  the  same  com- 
pounds that  are  produced  in  the  setting  of  Portland 
cement.  The  difference  in  its  action  is  explained  by 
the  fact  that  in  the  slow  cooling  of  Portland  cement 
the  salt  exists  in  crystalline  form,  while  through  the 
sudden  cooling  of  the  slag  it  is  made  vitreous,  and  is 
then  in  condition  to  be  attacked  by  the  lime. 

The  first  setting  of  Portland  cement  is  attributed  to 


54  HYDRAULIC   CEMENT. 

the  hydrating  of  the  aluminates  and  ferrites  of  lime, 
while  the  subsequent  hardening  is  due  to  the  slower 
progress  of  the  hydration  of  the  tricalcic  silicate.  The 
rapidity  of  set  is  therefore  dependent  upon  the  rela- 
tive proportions  of  aluminates  and  silicates.  When 
the  burning  is  done  at  a  low  temperature,  therefore, 
the  aluminates,  which  are  first  formed,  will  cause  a 
rapid  set,  while  as  the  degree  of  burning  becomes 
greater  the  aluminates  give  place  to  silicates  which 
cause  the  setting  to  become  slower  and  the  subse- 
quent gain  in  strength  greater.  The  aluminates  are 
thought  to  add  but  little  to  the  final  strength  of  the 
mortar,  as  they  are  not  permanent  compounds,  but  are 
acted  upon  by  water  and  various  salts  with  which  they 
are  likely  to  come  in  contact  in  the  work. 

Cements  of  low  hydraulic  index  harden  more  rapidly 
and  gain  their  full  strength  earlier  than  those  of  high 
index.  They  are  more  nearly  of  the  composition 
which,  according  to  the  theory,  should  give  the  highest 
proportion  of  active  ingredients,  while  those  of  high 
index  have  a  surplus  of  silica  and  alumina,  forming 
inert  material.  It  is  perhaps  questionable  whether  in 
all  cases  this  so-called  inert  material  is  in  reality  inert 
in  the  final  hardening  of  the  cement.  Sometimes 
those  cements  which  from  this  cause  harden  very 
slowly  continue  to  gain  in  strength  over  a  long  period, 
and  ultimately  surpass  those  which  gain  strength  more 
rapidly  in  the  beginning;  and  it  is  quite  possible  that 
this  overclayed  portion,  which  is  of  puzzolanic  char- 
acter, may  bear  an  important  part  in  the  final  harden- 
ing. 

Most    slow-setting  cements    have    a  period  during 


THE  SETTING  AND   HARDENING  OF  CEMENT.       55 

which  they  lose  strength  after  hardening  for  several 
months,  probably  due  to  the  decomposition  of  salts 
formed  by  the  parts  of  too  low  hydraulic  index  during 
the  burning.  This  loss  of  strength  is  usually  tem- 
porary when  the  cement  is  of  normal  composition;  but 
if  it  be  overlimed,  the  loss  of  strength  may  continue, 
to  the  final  destruction  of  the  mortar. 

The  experiments  of  M.  Candlot  indicate  that  the 
presence  of  carbonic  acid  is  essential  to  the  hardening 
of  hydraulic  cement-mortar.  He  found  that  if  the 
mortar  were  placed  in  distilled  water,  frequently 
renewed,  it  became  gradually  decomposed,  and  finally 
lost  all  coherence;  but  the  presence  of  carbonic  acid, 
as  is  common  in  all  natural  waters,  prevented  this 
action  and  caused  proper  hardening  to  take  place. 

ART.  21.     INFLUENCE  OF  CALCIUM  SULPHATE. 

The  action  of  sulphate  of  lime  to  slacken  the  rate  of 
setting  of  Portland  cement  is  well  known.  In  Ger- 
many it  has  been  common  to  utilize  it,  for  the  purpose 
of  regulating  the  rate  of  set,  by  adding  powdered 
gypsum  to  the  cement. 

M.  Candlot  *  has  made  a  careful  study  of  the  influ- 
ence of  sulphate  of  lime  upon  the  action  of  Portland 
cement.  He  found  that  the  increase  in  time  required 
to  set  varied  with  the  quantity  of  sulphate  added ;  an 
addition  to  a  quick  cement  of  from  I  to  4  per  cent 
being  sufficient  to  change  the  time  of  set  from  a  few 
minutes  to  several  hours.  Cement  which  has  been 

*  Ciment  et  Chaux  Hydrauliques  (Paris,  1891). 


$6  HYDRAULIC   CEMENT. 

made  slow-setting  by  the  addition  of  calcium  sulphate 
becomes  again  quick-setting  with  age,  more  or  less 
rapidly,  as  it  is  or  is  not  exposed  to  the  air.  In  some 
cases  the  cement  by  exposure  soon  becomes  quick- 
setting,  and  then  by  longer  exposure  again  becomes 
slow.  When  cement  treated  with  the  sulphate  of  lime 
has  regained  its  quick  action  by  exposure,  it  may  again 
be  made  slow  by  the  addition  of  a  small  quantity  of 
lime.  Fresh  cement  with  sulphate  of  lime  added,  and 
setting  slowly  in  consequence,  will  set  rapidly  if  the 
mortar  be  mixed  with  a  solution  of  the  carbonate  of 
soda. 

"  Cement  having  sulphate  of  lime  added  set  more 
rapidly  when  mixed  with  sea-water  than  with  fresh 
water,  and  that  which  had  been  exposed  and  regained 
its  former  activity  set  more  rapidly  when  mixed  wet 
than  when  mixed  stiff. 

"  The  addition  of  a  small  quantity  of  calcium  sul- 
phate to  Portland  cement  augments  the  strength. 
When  the  mortar  is  kept  in  sea-water  and  the  propor- 
tion of  sulphate  exceeds  I  or  2  per  cent,  the  mortar 
cracks  and  perhaps  disintegrates.  When  the  cement 
containing  the  sulphate  was  kept  in  sacks  during  several 
weeks  it  showed  less  strength  during  the  early  period 
of  hardening." 

M.  Candlot  concludes  from  his  experiments  that 
the  explanation  of  the  action  of  sulphate  of  lime  lies 
in  the  fact  that  in  the  presence  of  water  the  sulphate 
combines  with  the  aluminate  of  lirae  forming  the 
compouHd,  Al!1O3,3CaO,2.5(SO.1CaO),  which  crystal- 
lizes with  a  large  quantity  of  water.  The  action 
depends  upon  the  fact  that  the  aluminate  is  insoluble 


THE   SETTING   AND   HARDENING   OF  CEMENT.      57 

in  lime-water,  and,  as  most  of  the  quick-setting 
cements  contain  a  certain  quantity  of  free  lime,  when 
the  cement  is  gauged  the  lime  at  once  enters  into 
solution  and  prevents  the  action  of  the  aluminate  until 
the  sulphate  is  combined  with  it.  When  the  cement 
becomes  old,  the  free  lime  becomes  carbonized,  and 
fails  to  prevent  the  immediate  solution  of  the  alumi- 
nate. 

Aluminous  cements  burned  at  low  temperatures 
often  contain  considerable  aluminate  of  lime,  and  these 
may  bear  an  addition  of  5  to  10  per  cent  of  sulphate 
without  loss  of  strength.  The  proportion  of  sulphate 
must  always  be  limited  to  what  may  be  neutralized  by 
the  aluminates. 

ART.  22.     INFLUENCE  OF  CALCIUM  CHLORIDE. 

M.  Candlot  has  also  made  a  careful  study  of  the 
effect  upon  the  setting  and  hardening  of  cement-mor- 
tar of  chloride  of  calcium,  either  dissolved  in  the  water 
with  which  the  cement  is  mixed,  or  that  in  which  the 
mortar  is  immersed.  He  found  that  Portland  cement 
gauged  with  water  containing  a  few  grammes  per  litre 
of  chloride  of  calcium  sets  more  slowly  than  if  gauged 
with  pure  water;  while  if  the  solution  of  chloride  be 
concentrated,  100  to  400  grammes  per  litre,  the  set- 
ting is  very  rapid. 

"  The  influence  of  calcium  chloride  in  weak  solution 
upon  the  set  of  Portland  cement  may  be  attributed 
to  the  salts  which  determine  the  set  entering  into  solu- 
tion more  slowly  in  that  solution  than  in  pure  water. 
Hydrate  of  lime  agitated  with  a  large  excess  of  water 


§8  HYDRAULIC   CEMENT. 

is  dissolved  much  less  in  the  chloride  solution  than  in 
pure  water,  while  with  the  aluminate  of  lime  this 
result  is  much  more  marked. 

"  If  cement  of  Vassy,  quick-setting,  be  gauged  with 
a  solution  of  chloride  of  calcium,  20  to  40  grammes 
per  litre,  the  setting  is  about  the  same  as  with  pure 
water.  If  the  cement  be  diluted  to  a  fluid  with  the 
same  solution  it  will  not  set  or  harden.  Portland 
cement  treated  in  the  same  way  hardens  very  slowly, 
but  acquires  a  hardness  comparable  to  that  given  by 
fresh  water. 

"  Feeble  solutions  of  chloride  of  calcium  have  no 
appreciable  effect  upon  cements  exempt  from  alumina, 
like  certain  grappiers  cements  composed  almost  ex- 
clusively of  silicate  of  lime. 

"  From  this  the  conclusions  are  drawn: 

"  I.  That  in  Portland  cement  the  aluminate  exists  in 
feeble  proportions;  that  it  acts  in  an  energetic  manner 
upon  the  set,  but  very  little  upon  the  hardening,  which 
is  caused  by  the  silicate  of  lime. 

"2.  That  in  the  Vassy  cement  the  aluminate  of  lime 
is  the  essential  element,  and  determines  both  the  set- 
ting and  the  hardening;  the  role  of  the  silicate  being 
unimportant,  especially  during  the  early  period  of 
hardening. 

"3.  That  in  the  phenomena  of  setting  the  relative 
quantities  of  the  elements  present  determine  the 
action.  The  solution  of  chloride  in  presence  of  a  large 
quantity  of  the  aluminate  of  lime  perhaps  does  not 
hinder  the  hydration  and  crystallization;  but  if,  on  the 
contrary,  a  small  quantity  of  aluminate  be  mixed  in  an 


THE   SETTING   AND   HARDENING   OF   CEMENT.       59 

excess  of  chloride  solution,  the  action  of  that  prepon- 
derates, and  the  aluminate  will  not  enter  into  solution. 

'  A  weak  solution  of  CaCl  has  the  property  of  pro- 
voking the  rapid  hydration  of  lime.  A  cement  con- 
taining an  excess  of  free  lime,  gauged  with  pure  water, 
swells  and  disintegrates  under  the  slow  expansive 
action  of  the  free  lime.  The  same  cement  gauged 
with  a  solution  of  CaCI,  30  to  60  grammes  per  litre, 
does  not  swell,  because  the  lime  is  slaked  before  the 
set. 

44  As  already  stated,  when  Portland  cement  is  mixed 
with  a  solution  of  100  to  400  grammes  per  litre  CaCl 
it  sets  very  quickly.  This  set  is  accompanied  by  a 
strong  rise  in  temperature.  This  only  occurs  with  a 
fresh  cement.  With  an  old  cement  the  setting  re- 
mains slow,  no  rise  in  temperature  is  produced,  and 
the  mortar  swells  and  disintegrates. 

"  Mortar  of  cement  gauged  with  a  concentrated 
solution  of  CaCl  is  disintegrated  if  placed  in  water 
immediately  after  setting,  but  15  or  20  hours  after- 
ward it  may  perhaps  be  submerged  without  loss  of 
strength. 

"  The  action  of  a  concentrated  solution  CaCl  upon 
Portland  cement  is  due  to  the  fact  that  aluminate  of 
lime  is  attacked  very  energetically  by  that  solution. 
While  it  is  very  slightly  soluble  in  a  feeble  solution, 
it  is  dissolved  in  large  quantities  in  a  concentrated 
solution. 

"  When  a  fresh  cement  is  agitated  with  a  concen- 
trated solution  of  CaCl  it  dissolves  not  only  the  alu- 
minate, but  the  oxide  of  lime.  The  lighter  the  cement 
is  burned,  the  more  it  will  dissolve.  When  an  old 


60  HYDRAULIC  CEMENT. 

cement  is  agitated  with  the  concentrated  solution  of 
CaCl  the  aluminate  dissolves  but  very  little. 

ART.  23.     EFFECT  OF  SAND. 

Cement  is  ordinarily  employed  in  mortar  formed  by 
mixing  it  with  sand,  and  the  action  of  the  mortar  is 
necessarily  largely  affected  by  the  nature  and  quantity 
of  sand  used. 

When  the  cement  is  finely  ground  and  the  sand  of 
good  quality,  a  mortar  composed  of  equal  parts  of 
each,  as  a  general  thing,  finally  attains  a  strength  as 
high  as,  or  higher  than,  the  neat  cement.  Cements 
of  different  characters,  however,  vary  considerably  in 
their  power  to  "  take  sand  "  without  loss  of  strength; 
some  of  the  weaker  ones  may  not  be  able  to  take 
more  than  half  their  weight  of  standard  sand,  while 
others  can  be  mixed  with  considerably  more  than  their 
own  weight  without  loss  of  strength  at  the  end  of  one 
year  after  mixing.  All  have  a  certain  limit  within 
which  they  may  be  made  stronger  by  an  admixture  of 
good  sand  than  they  would  be  if  mixed  neat. 

Cement  mixed  with  sand  always  hardens  more  slowly 
than'  neat  cement,  and  requires  a  much  longer  time  to 
attain  its  maximum  strength.  As  the  proportion  of 
sand  to  cement  is  increased  both  the  rate  of  hardening 
and  final  strength  are  diminished.  Within  certain 
limits,  however,  the  strength  of  mortar  increases  over 
a  longer  period  of  time  as  the  proportion  of  sand 
becomes  greater,  and  as  the  time  of  observation  is 
extended  the  loss  of  strength  due  to  larger  propor- 
tions of  sand  becomes  less.  Thus  a  good  Portland 


THE   SETTING  AND   HARDENING  OF  CEMENT.      6l 

cement  in  a  mortar  containing  I  part  sand  to  I  of 
cement  at  the  end  of  a  year  may  be  expected  to  be 
stronger  than  mortar  of  neat  cement.  At  the  end  of 
three  years  the  I  to  I  mortar  should  be  much  stronger, 
while  a  2  to  I  may  be  as  strong  as  the  neat  mortar. 
At  the  end  of  four  or  five  years  the  2  to  I  mortar 
may  be  on  even  terms  with  the  i  to  I,  while  a  3  to  I 
mortar  may  have  steadily  gained  to  perhaps  three 
fourths  the  strength  of  the  others,  where  it  probably 
stops.  Beyond  the  limit  where  the  quantity  of  cement 
is  sufficient  to  fill  all  the  interstices  in  the  sand  the 
ultimate  strength  diminishes  very  rapidly  as  the  pro- 
portion of  sand  increases. 

Clean  and  sharp  sand  usually  gives  a  higher  strength 
in  mortar  than  that  containing  an  admixture  of  clay 
or  earth,  or  that  composed  of  rounded  grains.  Coarse 
sand  also  usually  gives  greater,  strength  than  that 
which  is  very  fine.  It  is  often  difficult,  however,  to 
judge  of  the  quality  of  sand  without  experimenting 
with  it.  In  some  cases  a  small  amount  of  fine  clay 
does  not  appear  to  injure  the  strength  of  the  mortar, 
while  a  judicious  mixture  in  the  sand  of  grains  of 
various  sizes  may  be  of  benefit,  through  reducing  the 
volume  of  interstices. 

A  mortar  composed  of  sand  and  cement  usually 
possesses  greater  ability  to  adhere  to  other  surfaces 
when  coarse  sand  is  used  than  if  the  sand  be  fine. 

ART.  24.     WATER  USED  IN  GAUGING. 

The  quantity  of  water  used  in  mixing  the  mortar  is 
one  of  the  most  important  conditions;  the  less  the 


62  HYDRAULIC   CEMENT. 

quantity,  provided  there  be  sufficient  to  thoroughly 
dampen  the  mass  of  cement,  the  quicker  will  be  the 
set.  With  some  Portland  cements,  changing  the 
quantity  of  water  used  in  mixing  neat  cement  from  20 
per  cent  to  25  per  cent  of  the  weight  of  cement 
doubles  or  even  triples  the  time  required  for  the 
mortar  to  set.  In  other  cases  the  effect  is  compara- 
tively slight. 

When  the  quantity  of  water  used  in  mixing  is  suffi- 
cient to  reduce  the  mortar  to  a  soft  condition  the 
hardening  as  well  as  the  setting  becomes  more  slow, 
and  the  strength  during  the  early  period  is  less  than 
if  a  less  quantity  be  used.  This  difference  disappears 
to  some  extent  with  time,  and  the  mortar  mixed  wet 
may  eventually  gain  nearly  as  much  strength  as  though 
mixed  with  less  water. 

When  the  quantity  of  water  employed  is  not  suffi- 
cient to  reduce  the  mass  to  a  plastic  condition,  the 
mortar  will  not  be  so  thoroughly  compacted,  and  will 
not  reach  the  same  strength  as  when  made  plastic, 
unless  pressure  be  applied  to  it.  But  if  just  sufficient 
water  be  used  to  thoroughly  dampen  the  mortar,  and 
pressure  be  applied  to  expel  the  air  and  close  the 
voids,  the  early  strength  will  be  greater  than  when 
more  water  is  used.  This  difference,  like  the  former 
one,  disappears  to  a  certain  extent  with  time,  but  the 
final  strength  is  usually  greater  with  the  less  quantity 
of  water. 

According  to  Prof.  Le  Chatelier,  the  solidity  of  the 
crystalline  mass  varies  with  the  form,  dimensions,  and 
mode  of  aggregation  of  the  crystals.  In  general,  the 
strength  of  a  single  crystal  is  greater  than  its  adher- 


THE   SETTING  AND   HARDENING  OF  CEMENT.      63 

ence  to  neighboring  crystals.  Long  needle-like  crystals 
give  greatest  strength,  and  crystals  have  this  character 
more  as  the  solution  is  more  strongly  supersaturated. 

The  nature  of  the  water  used  in  mixing  may  also 
affect  the  rate  of  setting.  When  sea-water  is  used  the 
setting  is  usually  slower  than  with  fresh  water,  the 
chloride  and  sulphate  of  magnesia  being  the  principal 
retarding  elements.  Cements  with  a  high  hydraulic 
index  show  a  less  difference  between  fresh  and  sea 
water  than  those  of  low  index,  and  well-burned  cem- 
ents less  than  imperfectly  burned  ones.  The  experi- 
ments of  M.  Candlot  indicate  that  this  is  due  to  the 
action  of  the  salts  mentioned  above  upon  the  aluminate 
of  calcium,  and  that  those  cements  containing  the 
highest  percentage  of  aluminate  are  affected  the  most 
by  being  mixed  with  sea-water. 

Water  containing  sulphate  of  lime  in  solution  retards 
setting  (see  Art.  21). 

Mortar  kept  immersed  in  sea-water  usually  hardens 
more  rapidly  than  that  kept  in  fresh  water.  This 
difference  is  commonly  much  more  noticeable  with 
neat  cement  than  with  mortar  containing  considerable 
proportions  of  sand.  The  strength  gained  in  sea- 
water,  however,  although  gained  much  more  quickly, 
is  generally  less  in  final  amount  than  that  in  fresh 
water.  There  is,  however,  a  very  great  difference 
between  various  cements  in  this  particular. 

Cements  with  a  low  hydraulic  index  show  the  great- 
est difference  between  sea  and  fresh  water.  Those 
containing  small  quantities  of  free  lime  give  much 
greater  early  strength  in  sea  than  in  fresh  water,  but 
are  also  sooner  disintegrated  by  the  action  of  sea-water. 


HYDRAULIC  CEMENT. 


ART.  25.     EFFECT  OF  ENVIRONMENT. 

Cement-mortar  kept  under  water  ordinarily  hardens 
more  rapidly  in  the  early  period  than  that  exposed  to 
the  air,  but  usually  that  kept  in  air  ultimately  reaches 
greater  strength.  The  highest  strength  is  commonly 
produced  by  keeping  the  cement  for  a  time  in  water, 
and  later  placing  in  dry  air.  Nearly  any  cement- 
mortar  will  harden  more  rapidly  and  attain  greater 
strength  if  kept  moist  during  the  operation  of  setting 
and  the  first  period  of  hardening  than  if  it  be  exposed 
at  that  time  to  dry  air.  A  sudden  drying  out  about 
the  time  of  completing  the  set  usually  causes  a  con- 
siderable loss  of  strength  in  mortar,  and  frequently 
the  mortar  so  treated  is  filled  with  drying  cracks. 
This  result  is  usually  more  marked  when  the  cement 
is  mixed  with  a  large  quantity  of  water  to  a  soft  con- 
dition. 

The  nature  of  the  water  in  which  the  mortar  is 
allowed  to  harden  is  of  more  importance  to  its  strength 
than  that  of  the  water  used  in  gauging.  When  the 
mortar  is  to  be  kept  in  air,  the  nature  of  the  water 
used  in  mixing  becomes  more  important,  although 
probably  the  variations  in  ordinary  natural  water  are 
rarely  sufficient  to  produce  any  appreciable  difference 
in  the  strength  of  the  mortar.  Mortars  gauged  with 
sea-water  harden  best  in  air. 

ART.  26.     EFFECT  OF  TEMPERATURE. 

The  temperature  of  the  water  used  in  mixing  has  an 
important  bearing  upon  the  time  required  for  setting; 


THE  SETTING  AND   HARDENING  OF  CEMENT.      65 

the  higher  the  temperature,  within  certain  limits,  the 
more  rapid  the  set.  Many  cements  which  require 
several  hours  to  set  when  mixed  with  water  at  a  tem- 
perature of  40°  Fahr.  will  set  in  a  few  minutes  if  the 
temperature  of  the  water  be  increased  to  80°  Fahr. 
Below  a  certain  inferior  limit,  ordinarily  from  30°  to 
40°  Fahr.,  the  mortar  sets  with  extreme  slowness  or 
not  at  all;  while  at  a  certain  upper  limit,  in  some 
cements  between  100°  and  140°  Fahr.,  a  change  is 
suddenly  made  from  a  very  rapid  to  a  very  slow  rate, 
which  then  gradually  decreases  as  the  temperature  in- 
creases, until  practically  the  mortar  will  not  set. 

The  temperature  of  the  cement,  and  that  of  the  air 
in  which  the  mortar  is  placed  during  setting,  influence 
the  rate  of  setting  in  about  the  same  manner  as  that 
of  the  water.  In  case  the  air  in  which  the  mortar  is 
placed  be  dry,  the  setting  will  usually  be  somewhat 
more  rapid  than  if  it  be  moist;  and  if  it  be  too  dry, 
the  rapid  evaporation  of  the  water  from  the  surface  of 
the  mortar  may  cause  drying  cracks  in  the  mortar. 

Quick-setting  cements  usually  show  a  rise  in  tem- 
perature during  setting,  due  to  the  rapidity  of  the 
action  which  takes  place.  It  has  been  suggested  that 
the  time  occupied  by  the  setting  would  be  better 
shown  by  observing  the  period  of  advanced  tempera- 
ture, than  by  noting  the  stiffening  of  the  mortar,  as 
is  common.  Most  slow-setting  cements,  however,  do 
not  show  sufficient  change  of  temperature,  if  any 
takes  place,  to  be  appreciable;  and  the  rise  in  tem- 
perature, where  it  does  take  place,  may  not  always  be 
the  result  of  the  process  of  setting. 

If  the  air  at  the  time  of  mixing  mortar  be  suffi- 


66  HYDRAULIC   CEMENT. 

ciently  cold  to  freeze  the  mortar  before  it  can  set,  it 
will  not  set  while  frozen;  but  most  cements  will  do  so 
after  thawing  out,  and  but  few  of  them  will  be  injured 
by  such  freezing  in  so  far  as  their  ultimate  strength  is 
concerned.  Recent  experiments*  have,  however, 
seemed  to  show  that  mortar  may  set  while  frozen  if  it 
remains  in  that  condition  fora  sufficient  length  of  time. 

The  temperature  of  the  water  with  which  cement- 
mortar  is  mixed  has  a  quite  appreciable  effect  both 
upon  its  rate  of  hardening  and  its  ultimate  strength, 
and  the  temperature  of  the  air  at  the  time  of  mixing 
has  a  similar  effect.  The  lower  the  temperature  at 
which  the  mixing  is  done,  the  slower  the  hardening 
and  the  greater  the  final  strength.  This  difference  is 
not  sufficient  to  be  important  at  ordinary  air  tempera- 
tures in  so  far  as  the  use  of  mortar  is  concerned,  but 
is  quite  appreciable  in  making  comparative  tests. 

The  temperature  of  the  air  or  water  in  which  the 
mortar  is  immersed  during  the  time  of  hardening  has 
a  very  appreciable  effect  upon  the  rate  of  hardening 
of  many  cements.  This  effect  differs  very  radically 
for  different  material ;  with  some  the  process  is  greatly 
accelerated  by  keeping  them  hot  as  compared  with 
what  would  be  the  result  in  cold  air  or  water;  others 
are  not  appreciably  affected,  while  still  others  seem  to 
be  retarded  in  their  hardening  by  the  application  of 
heat.  This  variation  is  to  be  found  among  cements 
of  the  same  class,  and  is  seemingly  independent  of 
their  value.  Cements  of  low  hydraulic  index  usually 
show  the  greatest  gain  in  rate  of  hardening  under  the 
action  of  heat. 

*  Paper  by  Cecil  B.  Smith;  Trans.  Canadian  Soc.  C.  E. 


THE   SETTING  AND   HARDENING  OF  CEMENT.       67 


ART.  27.     EFFECT  OF  AGE  UPON  CEMENT. 

The  effect  upon  a  cement  of  retaining  it  a  long  time 
before  using  depends  upon  the  nature  of  the  cement 
and  the  method  of  keeping.  When  the  cement  is 
enclosed  so  as  to  prevent  the  access  of  air,  as  in 
barrels,  it  may  usually  be  preserved  for  a  considerable 
time  without  experiencing  any  alteration,  provided  it 
is  kept  dry. 

When  exposed  to  the  air  the  cement  commonly 
undergoes  more  or  less  alteration.  Portland  cements 
of  good  quality  are  usually  but  slightly  affected,  as 
they  are  composed  for  the  most  part  of  stable  com- 
pounds. The  change  which  occurs  is  limited  usually 
to  making  the  cement  slower-setting.  Where  the 
cement  is  originally  slow-setting  this  effect  may  be 
very  slight,  and  the  cement  may  perhaps  be  retained 
for  a  long  period,  two  or  three  years  at  least,  without 
appreciable  change  in  its  properties.  A  hard-burned 
cement,  originally  quick-setting,  usually  becomes 
slower-setting  with  age,  but  commonly  without  injury 
as  to  its  ability  to  harden  and  its  ultimate  strength. 

Light-burned  cements,  particularly  Roman  cements, 
are  affected  in  much  greater  degree  by  age.  These 
cements  not  only  become  slower-setting  when  exposed 
to  the  air,  but  commonly  also  they  gradually  lose  the 
power  of  hardening  and  become  finally  inert — in  many 
cases  becoming  puzzolanic  material,  the  activity  of 
which  may  be  restored  by  the  addition  of  slaked  lime. 

The  changes  which  occur  in  cements  kept  in  dry  air 
are  attributed  to  the  action  of  carbonic  acid  upon  the 


68  HYDRAULIC   CEMENT. 

free  lime  which  they  may  contain,  and  perhaps  also 
upon  the  less  stable  compounds,  as  the  aluminates  of 
lime,  which  contribute  to  the  rapid  set  and  are  found 
most  plentifully  in  the  light-burned  material 

ART.  28.     EFFECT  OF  FINENESS. 

The  degree  of  fineness  to  which  the  cement  is  ground 
is  always  very  important  in  its  effect  upon  the  strength 
of  mortar  made  from  the  cement.  The  valuable  part 
of  the  cement  is  practically  only  that  portion  which  is 
ground  extremely  fine — to  an  impalpable  powder. 
The  coarse  parts  are  not  altogether  inert,  but  are  more 
or  less  active,  depending  upon  the  size  of  the  grains 
of  which  they  are  composed.  As  the  clinker  obtained 
in  burning  cement  is  very  dense  and  hard,  it  is  ground 
with  difficulty,  and  the  coarser  particles  are  apt  to  be 
of  the  best  burned,  and  therefore  most  valuable,  part 
of  the  material.  Coarse  grinding  is  likely  therefore  to 
leave  in  a  useless  condition  much  of  what  should  be 
the  most  active  portion  of  the  cement. 

The  rate  of  setting  is  accelerated  as  the  fineness  to 
which  the  cement  is  ground  becomes  greater.  In  a 
finely  ground  cement  the  amount  of  active  material  is 
greater  than  in  one  coarsely  ground,  and  the  chemical 
reactions  which  take  place  in  setting  are  facilitated  by 
fine  subdivision  of  the  particles.  When  the  cement 
is  gauged  with  sea-water  the  rate  of  setting  is  less  in- 
fluenced by  the  fineness. 

The  hardening  of  cement  mixed  neat  is  not  greatly 
affected  by  fineness;  that  finely  ground  usually  har 
dens  more  rapidly,  but  attains  less  final  strength  than. 


THE   SETTING  AND   HARDENING  OF  CEMENT.       69 

when  more  coarsely  ground.  The  hardening  of  the 
coarsely  ground  cements  is  more  gradual  and  regular, 
and  the  ultimate  strength  greater. 

Cement,  when  used,  is  commonly  mixed  with  sand, 
and  the  attainment  of  strength  in  sand-mortar  rather 
than  mortar  of  neat  cement  is  therefore  of  impor- 
tance. The  finer  ground  the  cement,  the  greater  its 
resistance  when  mixed  with  sand,  both  in  the  earlier 
and  later  stages,  and  also  the  sooner  will  it  reach 
its  ultimate  strength.  The  effect  of  fine  grinding  is 
much  greater  when  the  proportion  of  sand  to  cement 
is  large,  as  the  power  of  the  cement  to  take  sand 
without  diminution  of  strength  is  thereby  greatly  in- 
creased. The  coarser  particles  of  the  cement  may  be 
considered  as  practically  inert  material,  which  acts 
rather  as  sand  than  as  cement  in  the  mortar,  and  the 
power  of  the  cement  to  harden  and  develop  strength 
in  sand-mortar  is  thus  dependent  upon  the  amount  of 
fine  material  contained  in  it. 

The  adhesive  strength  of  cement  increases  very 
rapidly  with  the  fineness,  at  least  in  the  early  period 
of  hardening. 

The  difference  between  coarse  and  fine  grinding  is 
greater  in  the  early  period  of  hardening  than  later. 
The  fine  cement  hardens  much  more  rapidly,  but  the 
coarse  cement,  especially  in  rich  mortar,  often  reaches 
nearly  the  same  ultimate  strength.  The  attainment 
of  extreme  fineness  may  not  therefore  always  be  eco- 
nomical when  the  extra  cost  is  considered. 


CHAPTER  IV. 
THE  SOUNDNESS  OF  CEMENT. 

ART.  29.     PERMANENCE  OF  VOLUME. 

THE  permanence  of  any  structure  erected  by  the 
use  of  cement  is  dependent  upon  the  power  of  the 
cement,  after  the  setting  and  hardening  processes  are 
complete,  to  retain  its  strength  and  form  unimpaired 
for  an  indefinite  period.  Experiment  has  shown  that 
mortars  made  from  cement  of  good  quality  frequently 
continue  to  gain  in  strength  and  hardness  through  a 
period  of  several  years,  or  at  least  that  there  is  no 
material  diminution  of  strength  with  time;  and  that 
changes  of  temperature,  or  in  the  degree  of  moisture 
surrounding  it,  produce  no  injurious  effects  upon  the 
material.  This  durability  in  use  is  commonly  known 
as  \.\\Q  permanence  of  volume  or  soundness  of  the  cement. 

Heat  has  the  same  effect  in  causing  expansion  or 
contraction  of  cement-mortar  that  it  has  upon  other 
materials.  The  coefficient  of  expansion  for  neat 
Portland  cement,  according  to  a  series  of  experiments 
at  "  1'ecole  des  Ponts  et  Chaussees,"  is  about  the 
same  as  that  of  iron.  For  sand-mortar  the  coefficient 
is  somewhat  less. 

When  mortar  which  has  been  immersed  in  water  is 

70 


THE  SOUNDNESS  OF  CEMENT.  ?I 

transferred  to  dry  air  a  slight  contraction  may  take 
place  in  volume,  together  with  an  increase  in  strength, 
while  a  transference  the  other  way  may  produce  the 
opposite  result;  but  no  distortion  of  form  or  disinte- 
gration of  the  mortar  will  take  place  in  either  case  if 
the  cement  be  of  good  quality. 

Sometimes  cement  when  made  into  mortar  sets  and 
hardens  properly,  and  later,  when  exposed  to  the 
action  of  the  atmosphere  or  water,  becomes  distorted 
and  cracked,  or  even  entirely  disintegrated.  If  the 
composition  deviates  but  slightly  from  the  normal  this 
process  of  disintegration  may  not  show  itself  for  a  con- 
siderable time,  and  proceeds  very  slowly.  It  thus 
becomes  an  element  of  considerable  danger,  as  it  is 
liable  to  escape  detection  in  testing  the  cement. 

The  unsoundness  of  cement  may  be  occasioned 
either  by  defective  composition,  causing  the  mortar 
to  yield  to  the  action  of  expansions  proceeding  from 
within  itself,  or  by  exterior  agencies  which  act  upon 
ingredients  of  the  cement  susceptible  to  their  influ- 
ence, or  are  permitted  to  act  by  the  method  of  mak- 
ing and  using  the  mortar.  Very  little  is  definitely 
known  concerning  these  various  destructive  agencies, 
and  there  is  considerable  doubt  concerning  the  causes 
which  operate  in  many  instances.  The  expansive 
action  is  commonly  attributed  to  free  lime  or  magnesia. 
The  exterior  agencies  are  the  action  of  frost,  of  dry 
air  and  heat,  and  of  sea-water. 

Most  cements  probably  contain  small  amounts  of 
the  expansive  elements,  which  when  in  small  quantity 
act  with  extreme  slowness,  and  perhaps  produce  no 
visible  effect  for  several  months  after  the  use  of  the 


72  HYDRAULIC  CEMENT. 

mortar;  then  there  occurs  a  decrease  of  strength, 
which  probably  disappears  with  time.  Cements  of 
lew  index,  which  gain  strength  very  rapidly  in  the 
earlv  period,  are  quite  apt  to  act  in  this  manner,  and 
occasionally,  as  already  noted,  the  cement  may  not 
possess  sufficient  strength  to  resist,  and  the  expansive 
action  continues  to  ultimate  distintegration. 

The  term  Permanence  of  Volume,  if  limited  to  the 
power  of  the  material  to  resist  actual  change  of  form 
or  dimension  in  the  body  of  mortar,  is  not  necessarily 
synonymous  with  soundness,  if  by  soundness  we  desig- 
nate its  power  to  resist  disintegration  over  a  long 
period.  Most  unsound  cements  fail  by  swelling  and 
cracking  under  the  action  of  expansives.  In  some 
cements,  however,  the  failure  occurs  by  a  gradual 
softening  of  the  mass  of  mortar,  without  appreciable 
change  of  form  or  dimension,  the  process  being  very 
slow,  sometimes  not  noticeable  for  several  months 
after  the  mortar  is  mixed. 


ART.  30.     FREE  LIME. 

The  presence  of  small  quantities  of  free  lime  in  the 
cement  is  doubtless  one  of  the  most  frequent  causes 
of  disintegration  in  cement-mortar.  The  lime  being 
distributed  through  the  cement  in  small  particles  is 
hydrated  very  slowly  after  the  setting  of  the  cement, 
causing,  through  its  swelling  during  slaking,  a  strong 
expansive  force  on  the  interior  of  the  mortar,  and  pro- 
ducing an  increase  in  volume,  loss  of  strength,  and 
perhaps  final  disintegration. 


THE  SOUNDNESS  OF  CEMENT.          73 

The  effect  of  the  lime  depends  upon  its  physical 
condition,  and  is  affected  by  the  degree  of  burning. 

Lime  burned  at  a  high  heat  slakes  much  more 
slowly,  and  is  therefore  more  likely  to  be  injurious 
than  when  burned  at  a  low  temperature.  Prof.  Le 
Chatelier  found  that  where  the  addition  of  quicklime 
formed  by  burning  the  carbonate  produced  no  result, 
that  obtained  from  the.  nitrate  caused  swelling  and 
cracking  in  the  mortar.  The  presence  of  free  lime 
in  hard-burned  cements  of  low  index  is  therefore  of 
special  importance,  and  must  be  carefully  guarded 
against  by  securing  accurate  composition  and  com- 
plete reactions  in  burning. 

The  fineness  of  the  cement  also  modifies  the  action 
of  the  free  lime,  as  finely  divided  material  will  slake 
quicker  than  coarse  grains,  and  the  lime  is  more  apt 
to  become  hydrated  before  setting  is  completed ;  or  if 
the  cement  be  exposed  to  the  air  before  use,  the  lime 
in  a  fine  state  will  sooner  become  air-slaked. 

If  free  lime  be  present  in  such  condition  that  it 
becomes  slaked  before  the  initial  set  of  the  cement, 
it  causes  no  injury.  If  it  becomes  slaked  during  the 
setting  or  first  period  of  hardening,  the  strength  of  the 
mortar  may  be  reduced,  being  rendered  less  compact 
and  more  porous.  In  case  this  action  be  not  sufficient 
to  cause  disintegration  the  loss  of  strength  may  to  a 
great  extent  subsequently  disappear. 

When  the  slaking  of  the  free  lime  does  not  take 
place  until  a  longer  period  of  time  has  elapsed,  the 
danger  in  the  use  of  the  cement  is  more  serious. 
When  the  expansive  action  becomes  sufficient  to  over- 
come the  tenacity  of  the  mortar,  disintegration  ensues. 


74 


HYDRAULIC   CEMENT. 


If  the  expansive  action  be  not  sufficient  to  overcome 
the  tenacity  of  the  mortar,  an  increase  in  volume 
and  loss  of  strength  in  the  mortar  may  take  place,  the 
extent  of  which  is  dependent  upon  the  relative  inten- 
sities of  the  expansive  and  resisting  forces. 

These  effects  may  afterward  gradually  disappear,  but 
they  probably  have  the  effect  of  making  the  mortar 
more  easily  attacked  by  external  agencies.  Cements 
of  low  hydraulic  index,  which  gain  strength  rapidly  in 
the  early  period  of  hardening,  are  particularly  liable 
to  contain  appreciable  quantities  of  free  lime,  which  is 
frequently  shown  by  a  loss  of  strength  when  tests  are 
extended  over  a  considerable  period  of  time. 

Mortar  kept  under  water  is  acted  upon  much  more 
rapidly  than  that  exposed  to  dry  air. 


ART.  31.     MAGNESIA. 

Free  magnesia  in  cement  acts  very  much  like  free 
lime.  The  action  of  magnesia,  however,  is  much 
slower  than  that  of  lime,  and  for  this  reason  it  is  a 
more  serious  defect,  because  less  likely  to  be  detected 
in  the  tests  applied  before  using.  Prof.  Le  Chatelier 
mixed  5  per  cent  of  lime  and  of  magnesia  with  two 
samples  of  Portland  cement,  and  observed  the  time 
required  for  the  swelling  to  begin,  resulting  as  follows: 


Swelling  at  o°  C. 

Swelling  in  Water  at  100°  C. 

Commenced. 

Ended. 

Commenced. 

Ended. 

5*lime  
S%  magnesia. 

in  3  hours 
in  6  monhts 

36  hours 

immediately 
6  hours 

in  £  hour 
40  hours 

THE   SOUNDNESS   OF  CEMENT.  75 

In  hard-burned  cements  of  low  hydraulic  index  any 
magnesia  which  may  be  present  is  likely  to  be  in  a 
free  state,  and  hence  the  percentage  of  magnesia  in 
such  material  should  be  low,  and  specifications  fre- 
quently limit  the  amount  of  magnesia  that  may  be 
allowed  in  Portland  cement. 

When  mortar  fails  from  this  cause  the  expansive 
action  may  not  be  shown  for  several  months  after  the 
mortar  has  set,  and  then  in  a  comparatively  short  time 
the  swelling,  cracking,  and  disintegration  take  place. 

Dr.  Erdmenger  made  a  large  number  of  experiments 
upon  the  effect  of  adding  small  quantities  of  magnesia 
to  Portland  cement,  and  found  *  that  all  expanded  in 
water  and  contracted  in  air;  those  containing  consid- 
erable percentages  disintegrated,  beginning  after  about 
90  weeks. 

The  fineness  of  the  grains  of  magnesia,  like  those  of 
lime,  is  important  as  affecting  the  intensity  of  the 
effect.  Prof.  Le  Chatelier  found  that  where  magnesia 
coarsely  ground  produced  swelling  and  cracking,  the 
same  quantity  of  finely  ground  magnesia  produced 
swelling,  but  without  distorting  or  cracking  the  mortar. 
The  extent  of  the  change  in  volume  varies  with  the 
quantity  of  magnesia,  increasing  rapidly  as  the  quantity 
is  increased. 

The  expansion  is  reduced  as  the  mortar  is  mixed 
more  wet,  being  less  as  the  porosity  of  the  mortar  is 
greater. 

In  light-burned  cements  the  danger  of  free  mag- 
nesia is  greatly  lessened,  and  many  good  cements  of 

*  Journal  Society  of  Chemical  Industry,  vol.  xil.  p.  927. 


76  HYDRAULIC   CEMENT. 

this  class  contain  large  percentages  of  magnesia.  An 
overdose  may,  however,  be  an  element  of  danger  in 
.any  case,  and  several  failures  of  mortar  in  Europe 
have  been  attributed  to  magnesia  in  both  hard-burned 
and  light-burned  cements. 

M.  Durand-Claye  gives  an  instance  *  where  the 
cement  in  a  work  swelled  and  cracked,  and  an  exam- 
ination showed  that  it  contained  16  to  28  per  cent  of 
magnesia.  Experiments  were  made  by  mixing  mag- 
nesia with  good  cement,  and  swelling  resulted.  The 
rock  which  served  for  the  manufacture  of  the  cement 
contained  a  large  proportion  of  magnesia,  which  was 
probably  present  in  an  uncombined  state  in  the  cement. 
The  time  in  which  the  swelling  occurred  was  found  to 
depend  upon  the  amount  of  water  available.  When 
mixed  with  the  normal  quantity  and  left  in  dry  air  no 
expansion  took  place.  It  is  therefore  only  dangerous 
in  water. 

Analyses  of  this  cement  are  given  as  follows: 

Silicious     Silica.  Alumina.  Iron.  Lime.  Magnesia.   Sulphur.  Loss  on 

Sand.            %  %                %  %  %  %  Ignition. 

14.80  8.OO  4.60  47.30  24.30         0.60  0.40 

18.30  2.95  3.60  44.80  28.15         2.30          1.90 

0.35      20.70  3.35  3.65  43.30  26.70       0.15        i. So 

This  is  not  similar  to  the  magnesian  cements  com- 
monly used  in  the  United  States  on  account  of  the 
extremely  low  hydraulic  index.  If  it  be  assumed  that 
in  the  normal  cements  of  this  class  the  magnesia  acts 
like  lime  in  combining  with  silica  and  alumina,  the 
presence  of  free  magnesia  might  be  accounted  for  by 

*  Annales  des  Fonts  et  Chaussees,  1886,  vol.  I.  p.  845. 


THE  SOUNDNESS   OF  CEMENT.  77 

the   lack  of   a   sufficient  quantity  of  these  hydraulic 
elements. 

The  silicates  and  aluminates  of  magnesia  are  known 
to  possess,  like  those  of  lime,  the  property  of  harden- 
ing under  water.  Their  action,  however,  is  said  to 
be  much  slower  than  that  of  the  lime  salts,  and  it  has 
been  suggested  that  the  presence  of  the  magnesian 
salts  might  be  sometimes  injurious  on  account  of  their 
hydrating  after  the  hardening  of  the  lime  salts  in  the 
cement.  It  has  not  been  shown,  however,  that  any 
swelling  takes  place  in  the  setting  of  these  salts,  and 
the  effect  may  be  to  contribute  to  the  final  strength. 
Whatever  the  nature  of  the  process,  it  is  certain  that 
some  good  magnesian  cements  continue  to  increase  in 
strength  over  a  long  period,  the  proportionate  increase 
in  the  later  period  being  much  greater  than  for  Port- 
land cement  of  even  very  moderate  action. 

ART.  32.     ALUMINATE  OF  LIME. 

The  exact  role  of  aluminate  of  lime  is  in  many 
cases  a  matter  of  considerable  doubt.  M.  Bonnami 
considers  the  basic  aluminates  to  act  as  expansives  in 
hydrating  like  lime,  being  decomposed  in  presence  of 
water.  The  action  of  water  upon  these  aluminates  is 
very  rapid,  heat  being  given  off,  with  the  result  of 
greatly  accelerating  the  set  of  cements  containing  them 
in  appreciable  quantities. 

The  disintegration  of  mortar  has  in  certain  in- 
stances been  attributed  to  the  hydration  of  aluminates 
subsequent  to  the  set.  It  seems  probable,  however, 
that  where  the  aluminate  is  present  in  small  quan- 


?8  HYDRAULIC   CEMENT. 

titles  that  its  hydration  usually  takes  place  before  the 
setting  of  the  cement,  and  in  fact  is  the  first  cause 
of  the  setting  action. 

Aluminate  of  lime  is  freely  acted  upon  by  calcium 
sulphate,  as  stated  in  Art.  21,  forming  the  sulpho- 
aluminate  (3CaO.Al2O3 -f  2.sSO4Ca  -f-  6oH2O),  which 
crystallizes  with  great  expansive  force.  When  a 
cement  containing  aluminate  is  exposed  after  setting 
to  water  containing  calcium  sulphate  the  combination 
of  the  sulphate  with  the  aluminate  may  take  place,  with 
the  result  of  causing  swelling  and,  if  sufficient  in  quan- 
tity, disintegration  of  the  mortar. 

Aluminates  should  therefore  be  avoided  in  cements 
to  be  used  for  mortar  to  be  exposed  to  the  action  of 
sea-water,  as  the  sulphate  of  magnesia  acts  upon  the 
lime  of  the  cement,  forming  the  sulphate  of  lime,  which 
then  combines  with  the  aluminate  of  lime,  producing 
the  expansive  action.  For  this  reason  cements  high 
in  alumina  are  not  considered  desirable  for  marine 
work. 

ART.  33.     SULPHUR  COMPOUNDS. 

The  action  of  sulphur  in  cement  is  extremely  vari- 
able, depending  upon  the  state  in  which  it  may  exist 
and  the  nature  of  the  cement.  The  effect  of  adding 
sulphate  of  lime  for  the  purpose  of  rendering  the 
setting  slower  has  already  been  discussed  (Art.  21). 
This  action  depends  upon  the  presence  of  aluminate 
of  lime  in  sufficient  quantity  to  take  all  of  the  sulphur 
into  combination.  When  the  sulphate  is  added  in  ex- 
cess, or  to  a  cement  without  the  aluminate,  it  remains 


THE  SOUNDNESS  OF  CEMENT.          79 

soluble  in  the  mortar  and  is  gradually  dissolved  out, 
having  only  the  tendency  to  make  the  mortar  porous. 

It  is  pointed  out  by  M.  Candlot  that  if  the  aluminate 
be  prevented  from  acting  by  adding  slaked  lime  to  a 
cement  with  which  sulphate  of  lime  has  been  mixed, 
the  combination  of  the  sulphate  and  aluminate  may 
take  place  after  setting,  causing  the  destruction  of  the 
mortar  through  its  expansive  action. 

The  effect  of  the  existence  of  sulphate  in  the 
material  before  burning  the  cement  may  be  quite 
different  from  that  of  adding  it  afterward.  In  Roman 
cement  the  two  seem  to  give  analogous  results;  but  in 
the  heavily  burned  cements  it  may  be  in  a  state  not 
readily  soluble,  and  hence  slow  in  acting  upon  the 
aluminate,  thus  causing  the  expansion  to  be  delayed 
until  after  the  set. 

Mr.  Spachman,  who  experimented  upon  the  pro- 
duction of  Portland  cement  from  alkali  waste,  con- 
cludes *  that  the  danger  in  using  material  containing 
too  large  proportions  of  sulphate  of  lime  is  due  to  the 
likelihood  of  forming  calcium  sulphide,  CaS,  during  the 
burning,  which  afterward  forms,  with  the  iron  oxide  of 
the  cement,  the  sulphide  of  iron,  FeS.  This  upon 
exposure  is  oxidized  to  a  sulphate  of  iron,  changing 
the  color  of  the  cement  to  a  brown,  and  causing  it  to 
lose  much  of  its  activity,  in  some  instances  scarcely 
setting  at  all.  Mr.  Spachman  gives  the  limit  of  about 
5#  of  SO4Ca  as  what  may  be  safely  used. 

Prof.  Tetmajer  states  that  calcium  sulphate  in  Port- 
land cement  sometimes  acts  as  an  expansive,  through 

*  Journal  Society  of  Chemical  Industry,  vol.  xi.  p.  497. 


80  HYDRAULIC   CEMENT. 

the  fact  that  it  is  readily  oxidizable  and   expands  in 
oxidation. 

In  slag-cements  the  presence  of  calcium  sulphide 
is  thought  to  be  less  injurious.  According  to  M. 
Prost,  it  gives  a  green  color  to  the  cement  when  kept 
in  water,  but  without  injury  to  its  strength.  In  the 
air  it  may  cause  the  mortar  to  crack. 

ART.  34.     EXTERIOR  AGENCIES. 

The  principal  exterior  agencies  which  operate  to 
cause  the  destruction  of  mortar  are  changes  in  tem- 
perature or  in  humidity,  and  the  nature  of  the  water 
with  which  it  may  be  in  contact.  Exterior  mechani- 
cal agencies,  such  as  the  shocks  of  waves  or  of  ice  and 
sand  produced  by  a  current,  have  an  abrasive  action 
and  may  overtax  the  strength  of  mortar  in  the  early 
period  of  hardening,  but  they  do  not  cause  disintegra 
tion  through  injury  to  the  cement. 

The  effect  of  frost  is  to  set  up  a  mechanical  action 
through  the  freezing  of  water  in  the  pores  of  the  mor- 
tar and  resistance  to  it  probably  depends  mainly  upon 
the  strength  of  the  mortar  and  its  ability  to  resist  this 
expansion. 

The  nature  of  the  water  to  which  the  mortar  is  ex- 
posed is  important  because  of  the  possible  chemical 
action  of  salts  which  it  may  hold  in  solution.  This  is 
shown  by  the  disintegration  of  mortar  in  sea-water  or 
in  sewer  water  which  is  quite  sound  when  subjected 
to  fresh  water. 

According  to  M.  Candlot,  "  all  hydraulic  materials 
are  alterable  by  pure  water.  A  mortar  traversed  by 


THE   SOUNDNESS   OF   CEMENT.  8 1 

pure  water  finally  loses  all  coherence,  the  elements 
constituting  the  agglomerant  being  little  by  little 
decomposed.  But  natural  water  contains  always  car- 
bonic acid,  which  intervenes  in  the  majority  of  cases  to 
arrest  decomposition  and  close  the  pores  of  the  mortar 
traversed  by  the  water.  When  the  cement  does  not 
give  up  its  lime  too  readily  the  lime  is  transformed 
into  carbonate,  which  forms  a  deposit  in  the  voids  of 
the  mortar.  If,  on  the  contrary,  the  dissolving  of  the 
lime  in  the  water  which  traverses  the  mortar  is  abun- 
dant, there  is  produced  a  large  quantity  of  carbonate 
without  cohesion,  which  is  carried  off  by  the  water." 

In  regard  to  the  effect  of  temperature  Prof.  Le 
Chatelier  says:  "  At  elevated  temperatures  certain 
solid  hydrates  lose  their  water  and  are  reduced  to 
powder,  like  the  crystalline  carbonate  of  soda,  and 
cause  the  disintegration  of  the  mortar.  This  is  the 
case  with  certain  aluminates  of  lime,  especially  the 
alumino-sulphate,  but  precise  experiments  are  still 
necessary  upon  this  subject. 

'  This  dehydration  occurs  in  dry  air.  This  explains 
the  well-known  fact  that  certain  cements  stay  for 
months  in  water  and  attain  high  strength,  but  the 
same  exposed  to  dry  hot  air  disintegrate  into  a  sandy 
mass." 

M.  Candlot  says  that  "  aluminous  cements  are 
subject  to  alteration  in  surroundings  exposed  to  alter- 
nate dryness  and  humidity,  and  also  when  exposed  to 
a  high  temperature."  It  should  be  remarked,  how- 
ever, that  this  probably  depends  upon  the  alumina 
b~ing  present  as  basic  aluminate  of  lime,  and  that 
cements  with  a  high  proportion  of  alumina,  such  as 


82  HYDRAULIC   CEMENT. 

certain  Roman  cements,  containing  considerable  sul- 
phate, commonly  give  good  results  when  used  in 
situations  exposed  to  changes  in  humidity.  The 
Louisville  cements  are  a  prominent  example  of  this. 

When  cement-mortar  during  the  early  period  of 
hardening  is  exposed  to  very  dry  air,  the  hardening 
may  be  interfered  with  by  the  lack  of  moisture  neces- 
sary to  admit  of  the  completion  of  the  hydration  and 
crystallization  of  the  cement,  thus  causing  a  lack  of 
cohesive  strength,  and  perhaps  ultimate  destruction  of 
the  mortar.  Different  cements  vary  greatly  in  the 
extent  to  which  they  are  influenced  by  this  cause; 
slow-setting  Portland  cements  being  ordinarily  least 
and  the  slag-cements  most  affected. 

ART.  35.     EFFECT  OF  SEA-WATER. 

The  destructive  effect  of  sea-water  upon  hydraulic 
mortars  which  are  sound  in  fresh  water  is  probably 
due  to  the  action  of  magnesian  salts  upon  the  lime  of 
the  cement,  thus  forming  sulphate  and  chloride  of 
calcium.  The  action  of  these  salts  upon  the  harden- 
ing of  cement-mortars  has  already  been  discussed. 

When  mortar  in  sea-water  fails  by  swelling,  the 
failure  is  usually  attributed  either  to  too  large  a  pro- 
portion of  free  lime  or  magnesia,  or  to  aluminate  of 
lime  in  the  cement.  When  the  cement  contains  free 
lime,  the  expansive  action  is  greatly  intensified  in  sea- 
water  as  compared  with  that  in  fresh  water.  This 
may  be  explained  by  the  presence  of  calcium  chloride, 
which  increases  the  rapidity  of  slaking  of  quicklime, 
causing  the  expansion  to  be  shown  sooner,  and  to  act 


THE   SOUNDNESS   OF   CEMENT.  83 

more  violently  than  in  fresh  water.  When  the  cement 
contains  considerable  aluminate  of  lime  the  calcium 
sulphate  may  act  upon  it,  as  indicated  in  Art.  32, 
causing  the  formation  of  the  sulpho-aluminate  and  the 
corresponding  expansive  effect. 

When  mortar  made  from  cement  of  good  quality  is 
exposed  to  the  action  of  sea-water  its  durability 
depends  largely  upon  the  permeability  of  the  mortar. 
The  lime  salts  formed  by  the  action  of  sea-water  are 
readily  soluble,  and  if  the  mass  is  freely  permeated 
by  water  those  salts  may  be  washed  out,  leaving  the 
mortar  more  open  to  the  action  of  the  disintegrating 
agencies.  Thus  mortar  of  any  Portland  cement  may 
be  injuriously  affected  by  sea- water  if  used  in  such 
manner  as  to  permit  the  continuous  action  of  the  mag- 
nesian  salts  through  the  mass. 

The  ultimate  hardening  of  mortar  in  sea-water,  as 
in  fresh  water,  seems  to  depend  upon  the  action  of 
carbonic  acid  in  forming  a  protection  to  prevent  the 
operation  of  the  elements  of  disintegration.  When 
the  mortar  resists  the  penetration  of  the  water  so  as 
to  prevent  its  renewal  in  the  interior  of  the  mass,  the 
outside  soon  becomes  protected  by  the  action  of  the 
carbonic  acid,  and  effectually  prevents  further  action 
of  the  magnesian  salts. 

M.  Durand-Claye  examined  the  mortar  from  a  sea- 
wall where  parts  of  it  were  disintegrated,  and  found  a 
large  proportion  of  magnesia,  although  it  was  not  con- 
tained in  the  original  rnortar  or  in  the  portions  of  the 
wall  which  were  still  sound.  The  percentage  of  sul- 
phuric acid  was  also  increased  in  the  disintegrated 
portions,  seeming  to  show  that  the  magnesia  had  been 


84  HYDRAULIC   CEMENT. 

precipitated  from  the  sulphate  of  the  sea-water,  and 
the  resulting  sulphate  of  lime  had  for  the  most  part 
washed  out. 

Where  the  water  against  the  wall  is  under  pressure 
from  one  side,  or  where  tidal  flow  keeps  the  work  sub- 
merged only  a  part  of  the  time,  the  action  of  the  sea- 
water  is  more  strongly  felt  than  in  work  always  en- 
tirely covered. 

M.  Alexander  submitted  blocks  of  cement-mortar 
to  the  filtration  of  both  fresh  and  sea  water.*  Those 
in  fresh  water  were  unaffected,  but  those  in  sea-water 
were  disintegrated  in  six  months.  Analysis  showed 
that  those  in  fresh  water  suffered  a  slight  loss  of  lime 
and  sulphuric  acid,  while  those  in  sea- water  were  much 
changed  by  loss  of  lime  and  gain  in  magnesia  and  sul- 
phuric acid. 

M.  Alexandre  also  found  that  "  argillaceous  or  soft 
calcareous  sand  is  attacked  by  sea-water,  and  mortar 
containing  them  may  be  decomposed  although  the 
cement  is  good." 

*  Annales  des  Fonts  et  ChaussSes,  1890,  vol.  i.  p.  408. 


CHAPTER   V. 
METHODS  OF  TESTING  CEMENT. 

ART.  36.     OBJECT  OF  TESTS. 

TESTS  of  cement  may  have  for  their  object  either 
the  examination  of  the  quality  of  the  material  in 
order  to  determine  its  fitness  for  use,  or  investigation 
of  the  properties  of  the  cement  for  the  purpose  of  in- 
creasing knowledge  of  its  behavior  under  the  varying 
contingencies  of  use.  Where  experiments  are  made 
with  this  latter  object,  the  tests  to  be  applied  and 
methods  of  operation  must  of  course  be  dependent 
upon  the  special  point  to  be  investigated. 

In  many  instances  it  may  be  possible  to  combine 
to  a  certain  extent  the  two  objects.  This  is  particu- 
larly the  case  where  a  permanent  laboratory  is  estab- 
lished to  regulate  the  reception  of  material  for  exten- 
sive works,  as  in  the  case  of  the  laboratories  connected 
with  the  Government  experiment  stations  in  Europe. 
In  some  of  these  stations  careful  examination  of  every 
sample  of  cement  in  a  number  of  particulars  is  made, 
with  the  result  of  accumulating  a  mass  of  valuable  in- 
formation regarding  the  characteristics  of  all  the  differ- 
ent kinds  of  cement.  Systematic  series  of  tests  of  this 
character  possess  much  greater  value  as  a  means  of 

85 


«6  HYDRAULIC    CEMENT. 

deducing  the  laws  governing  the  action  of  the  mortar 
than  special  examinations  upon  particular  points, 
which  often  fail  to  take  into  account  the  variable 
nature  of  the  material,  and  the  necessity  for  exact 
knowledge  of  the  nature  of  the  cement  upon  which 
the  tests  are  made. 

The  French  "  Commission  upon  the  Method  of 
Testing  the  Materials  of  Construction"  recommend 
that  in  the  permanent  laboratories  cement  should  be 
systematically  tested  in  the  following  particulars: 
Chemical  analyses;  fineness;  specific  gravity;  appar- 
ent density;  homogeneity;  time  of  setting;  tensile, 
compressive,  flexural,  and  adhesive  strength;  perma- 
nence of  volume;  porosity;  permeability;  resistance 
to  decomposition  by  sea- water;  and  yield  of  mortar. 

Tests  of  cement,  as  commonly  made  for  its  recep- 
tion upon  engineering  work,  have  for  their  object  only 
the  determination  of  the  quality  of  the  material  and 
its  fitness  for  the  use.  Tests  for  this  purpose  must 
be  made  according  to  some  recognized  standard,  and 
cannot  closely  approximate  the  conditions  of  use  with- 
out impairing  their  value  as  means  of  judging  the 
quality  of  the  cement.  What  it  is  necessary  to  know 
about  the  cement  is  that  it  will  set  and  harden  into  a 
solid  mass,  which  will  firmly  adhere  to  any  surface 
with  which  it  may  be  in  contact,  and  that  it  will  en- 
dure through  a  long  time  without  change  of  form  or 
loss  of  solidity. 

As  ordinary  tests  must  be  made  in  a  short  time,  but 
a  few  days  at  most  being  usually  allowed  for  determin- 
ing the  quality  of  the  material,  the  problem  to  be  met 
in  testing  is  to  apply  such  tests  as  will  enable  a  pre- 


METHODS  OF  TESTING  CEMENT.  87 

diction  to  be  made,  from  its  behavior  under  them  in 
a  short  time,  as  to  what  it  will  do  in  a  long  time  under 
the  circumstances  of  its  use.  The  difficulty  of  this 
with  a  material  varying  so  greatly  in  character  and 
in  its  behavior  under  various  conditions  is  evident. 
Having  a  particular  brand  of  cement  whose  character- 
istics are  known,  it  may  readily  be  determined  whether 
a  given  sample  is  of  normal  quality,  and  something 
may  be  predicted  of  its  future  from  its  behavior  under 
short-time  tests.  Very  little,  however,  can  be  done 
.in  the  way  of  generalization,  and  for  a  new  and  un- 
known material  it  is  only  possible  to  state  a  somewhat 
indefinite  probability  as  to  final  results. 

Tests  may  be  imposed  which  in  nearly  all  cases 
will  secure  good  material,  but  often  at  the  expense  of 
rejecting  equally  good  or  better  material.  This,  how- 
ever, will  be  unavoidable  until  the  characteristics  of 
the  various  brands  of  cement  are  more  fully  known, 
and  the  tests  to  which  each  should  be  subjected  better 
understood. 

The  tests  which  are  usually  imposed  to  determine 
the  quality  of  hydraulic  cement  are  those  of  weight, 
fineness,  time  of  setting,  tensile  strength,  and  sound- 
ness. Chemical  analysis  is  sometimes  made,  and  spe- 
cific-gravity test  is  substituted  for  that  of  weight,  or 
both  are  frequently  omitted.  Compression-tests  are 
also  sometimes  added. 

The  greatest  weight  is  usually  given  to  the  test  of 
tensile  strength,  and  much  greater  value  is  commonly 
placed  upon  the  results  of  that  test  than  they  deserve. 
It  is  much  the  simplest  and  best  means  of  making  a 
test  for  strength,  and  is  very  desirable  as  showing  the 


88  HYDRAULIC   CEMENT. 

proper  hardening  of  the  mortar,  but  cements  cannot 
be  graded  in  value  by  the  strength  attained  in  a  short 
time.  Cement  giving  high  early  strength  is  to  be 
relied  upon  only  in  so  far  as  it  has  been  shown  by  ex- 
perience capable  of  subsequently  maintaining  such 
strength.  The  attempt  to  produce  cement  which  will 
develop  great  strength  on  short-time  tests  is  liable  to 
result  in  lowering  the  hydraulic  index,  or  the  addition 
of  calcium  sulphate,  and  sometimes  in  the  presence  of 
free  lime,  giving  a  material  more  likely  to  be  unsound 
than  one  of  more  moderate  strength. 

The  test  for  soundness  or  permanence  of  volume  is 
an  important  one,  as  giving  an  indication  of  the  prob- 
able durability  of  the  material;  but  in  this,  as  in  the 
other  tests,  a  knowledge  of  the  usual  action  of  the 
material  will  contribute  greatly  to  the  proper  inter- 
pretation of  the  test. 

The  test  for  fineness  is  also  important  as  bearing 
upon  the  power  of  the  cement  to  take  sand. 

It  was  recommended  by  the  committee  of  the 
American  Society  of  Civil  Engineers  upon  a  uniform 
system  of  testing,  that  tests  for  quality  be  limited  to 
the  above  three  most  important  tests — fineness,  tensile 
strength,  and  soundness;  and  this  recommendation  is 
now  commonly  followed  in  the  United  States,  although 
the  test  for  soundness  as  usually  made  is  of  little  value. 

ART.  37.     APPARENT  DENSITY. 

The  apparent  density  of  cement  is  measured  by 
determining  the  weight  of  a  given  volume  of  the 
material.  This  test  is  made  as  a  means  of  showing 


METHODS   OF  TESTING   CEMENT.  89 

whether  the  process  of  manufacture  has  been  well  con- 
ducted. If  the  cement  be  not  thoroughly  burned  or 
if  it  lack  homogeneity  so  that  in  portions  of  it  the 
combinations  are  not  complete,  the  weight  is  less  than 
when  the  material  is  homogeneous  and  well  burned. 
Variations  of  composition  also  affect  the  weight,  so 
that  there  may  be  considerable  variations  in  the  weight 
of  various  cements  of  good  quality,  equally  well 
burned. 

The  apparent  density  is  affected  by  the  fineness  to 
which  the  cement  is  ground ;  the  coarser  the  particles 
of  the  cement,  the  greater  its  weight  per  unit  volume. 
The  weight  test  when  employed  should  therefore  be 
combined  with  one  for  fineness  to  prevent  the  attain- 
ment of  heavy  weight  by  coarse  grinding. 

The  test  for  apparent  density  is  not  usually  em- 
ployed for  the  reception  of  material,  as  it  is  somewhat 
indefinite  in  result.  It  is,  however,  sometimes  in- 
cluded in  specifications  in  England,  and  is  used  in 
many  European  laboratories  where  a  careful  study  is 
made  of  the  properties  of  cement. 

As  the  cement  powder  may  be  packed  in  the  meas- 
ure so  as  to  give  very  different  weights  for  the  same 
volume,  it  is  necessary  to  use  a  uniform  method  of 
filling  the  measure  in  determining  the  weight.  The 
common  method  of  conducting  the  test  is  to  pass  the 
powder  through  a  sieve  and  allow  it  to  fall  through  a 
funnel  or  down  an  inclined  plane  through  a  given 
height  into  a  measure,  which  when  full  is  struck  and 
weighed.  The  height  of  fall  and  the  size  of  the  meas- 
ure both  affect  the  result,  the  cement  packing  closer 
in  a  large  than  in  a  small  measure. 


(JO  HYDRAULIC   CEMENT. 

In  Europe  several  appliances  are  used  for  testing 
apparent  density. 

Tetmajer's  Apparatus.  —  The  apparatus  of  Prof. 
Tetmajer  is  used  in  a  number  of  the  leading  labora- 
tories. It  is  shown  in  Fig.  i,  and  consists  essentially 


FIG.  j. 

of  a  cylindrical  measure  (M)  of  I  liter  capacity  and  10 
centimeters  high,  provided  with  ears  which  catch  upon 
a  frame  formed  of  two  levers  (Z,).  The  frame  is  raised 
and  dropped  at  each  turn  of  the  hand-wheel  by  the 
cam  (O),  thus  giving  a  succession  of  jars  to  the  meas- 
ure. 

Above  the  measure  a  sieve  (7?)  is  oscillated  upon  a 
system  of  levers  which  are  hinged  to  the  base,  and 
moved  by  the  rod  (V),  giving  two  oscillations  at  each 
turn  of  the  hand-wheel.  The  number  of  revolutions 
is  recorded  by  the  revolution-counter  (T). 

In  the  operation  of  the  apparatus  the  cement  is 
filled  into  the  sieve  and  shaken  through  by  the  oscil- 
lations produced  by  turning  the  hand-wheel.  It  is 
caught  in  the  measure  and  jarred  down  by  the  raising 
and  dropping  of  the  frame.  About  500  revolutions 


METHODS   OF  TESTING   CEMENT.  9! 

are  necessary  to  secure  the  best  results  in  compacting 
the  powder  in  the  measure.  The  compactness  is  found 
to  vary  with  the  rapidity  of  motion,  a  moderate  speed 
of  about  200  revolutions  per  minute  giving  a  maximum 
effect,  and  being  considered  most  desirable. 

Inclined-plane  Apparatus. — The  inclined-plane  ap- 
paratus for  apparent  density  has  been  used  in  a  num- 
ber of  forms,  one  of  which,  employed  in  France  and 
recommended  by  the  "  Commission  des  Methodes 
d'Essai  des  Materiaux  de  Construction,"  is  repre- 
sented in  Fig.  2. 


FIG.  2 

The  inclined  plane  is  formed  of  sheet  zinc  30  cm. 
long  and  inclined  at  45°  with  the  horizontal.  It  is  10 
cm.  wide  for  the  upper  two  thirds  of  its  length,  and 
through  the  lower  third  diminishes  gradually  to  5  cm. 
at  the  lower  end.  The  zinc  is  turned  up  at  the  sides 
to  form  a  channel  in  which  the  material  may  slide. 


92  HYDRAULIC  CEMENT. 

At  the  point  where  the  larger  plane  begins  to  narrow 
a  second  sheet  of  zinc,  20  cm.  long  and  10  cm.  wide, 
is  set  at  right  angles  to  the  first,  leaving  an  opening  of 

1  cm.     The  measure  10  cm.  high  and  of  I  litre  capacity 
is  placed  with  its  top  5  cm.  below  the  lower  edge  of 
the  plane. 

The  cement  is  poured  in  small  quantities  on  the 
summit  of  the  secondary  plane  so  slowly  as  not  to 
clog  the  opening  between  the  planes,  until  the  meas- 
ure is  full  when  it  is  struck  and  weighed. 

A  single  inclined  plane  of  somewhat  greater  length 
(50  cm.)  is  sometimes  used,  the  cement  being  sifted 
upon  the  upper  end  and  allowed  to  slide  directly  into 
the  measure.  It  is  said,  however,  to  give  less  uniform 
results  than  the  double  plane  unless  handled  with 
extreme  care. 

German  Funnel  Apparatus. — This  apparatus  was 
recommended  by  the  German  conference  upon 
methods  of  testing  materials,  as  was  also  the  Tetmajer 
apparatus. 

The  funnel  is  formed  of  a  hollow  cone  with  its  axis 
vertical,  as  shown  in  Fig.  3.  The  height  of  the  cone 
is  1 8  cm.,  its  upper  base  is  20  cm.  and  lower  base 

2  cm.  in  diameter,  terminated  at  the  lower  end  by  a 
second  cone  5  cm.  high,  with  a  lower  base  1.6  cm.  in 
diameter.     The  funnel  is  supported   upon    a  tripod, 
with  its  lower  end  20  cm.  above  the  table  and  10  cm. 
above  the  top  of  the  liter  measure.     To  facilitate  the 
flow  of  cement  into  the  measure  a   rod  7/10  cm.  in 
diameter  is  rotated  in  the  axis  of  the  funnel.     This 
rod  is  guided  by  two  cross-rods  supported   upon  the 
interior  surface  of  the  funnel. 


METHODS   OF   TESTING   CEMENT. 


93 


In  the  operation  of  this  apparatus  sufficient  cement 
to  fill  the  measure  is  placed  in  the  funnel,  and  the  rod 
is  then  rotated,  about  45  revolutions  per  minute,  by 
gear  or  by  hand  until  the  material  has  passed  through 


FIG.  3. 

and    filled    the    measure,   which  is    then    struck   and 
weighed. 

Sieve  and  Funnel  Apparatus. — This  apparatus  as 
used  in  France  is  shown  in  Fig.  4.  It  consists  of  a 
funnel  with  a  sieve  fitting  into  the  upper  part  of  it 
and  the  measure  below.  The  cement  is  put  into  the 
sieve,  and  gradually  worked  through  by  the  use  of  a 
spatula.  It  then  slides  down  the  funnel  into  the 
measure  until  that  is  filled. 


94 


HYDRAULIC   CEMENT. 


The  "Commission  des  Methodes  d'Essai  des  Mate- 
riaux  de  Construction"  made  a  careful  comparison  of 
results  obtained  by  the  various  methods.  They  found 
the  German  funnel  apparatus  quite  precise  in  its 


FIG.  4. 

results  with  certain  materials,  but  that  with  some 
cement  it  always  became  clogged  by  the  packing  of 
the  material  in  the  funnel.  The  Tetmajer  apparatus 
is  capable  of  great  precision,  but  is  somewhat  compli- 
cated, and  requires  careful  manipulation  to  secure 
always  the  same  rate  of  filling  the  measure  and  the 
same  amount  of  compacting.  The  inclined  plane  and 
the  sieve  and  funnel  apparatus  are  found  to  give  good 
results,  and  are  recommended  by  the  commission  for 


METHODS  OF  TESTING  CEMENT.  95 

use  in  France.  The  two  latter  give  nearly  identical 
results,  the  German  apparatus  somewhat  higher  and 
the  Tetmajer  apparatus  much  larger  results  than  the 
others. 

The  following  method  for  apparent  density  was 
recommended  in  the  preliminary  report  of  the  com- 
mittee of  the  American  Society  of  Civil  Engineers 
upon  cement  testing,  but  has  never  come  into  com- 
mon use: 

"  Procure  a  cylinder  of  a  height  of  6  inches,  having 
an  interior  area  of  2  square  inches.  Sifting  the  cem- 
ent to  be  measured  so  that  it  may  not  be  compact, 
weigh  carefully  5  ounces  if  of  Portland  cement  and  4 
ounces  if  of  natural  cement,  and  pour  the  same  into 
the  cylinder,  which  should  stand  upright  with  its 
lower  end  resting  upon  a  close-fitting  and  suitable 
base;  then,  without  shock  or  sudden  impact,  lower  a 
close-fitting  piston,  moving  without  friction,  slowly 
down  the  cylinder  on  to  the  cement;  said  piston  and 
its  attachments  to  weigh  50  pounds.  After  resting 
thereon  one  minute,  remove  the  same  and  ascertain 
the  bulk  of  cement  thus  compressed." 

In  making  tests  for  apparent  density  it  is  advisable 
to  sift  the  cement,  and  use  only  that  portion  which 
passes  the  finest  sieve,  thus  making  the  result  to  a 
certain  extent  independent  of  the  fineness  of  grinding. 
To  accomplish  this  the  sieve  used  should  be  as  fine  as 
possible  in  order  to  eliminate  all  but  the  impalpable 
powder.  In  Europe  a  sieve  of  5000  meshes  per  square 
centimeter  is  employed  for  this  purpose,  correspond- 
ing to  the  No.  1 80  sieve,  32,400  meshes  per  square 
inch. 


96  HYDRAULIC  CEMENT. 

The  ordinary  weight  of  Portland  cement  varies  from 
70  to  100  Ibs.  per  cubic  foot,  depending  largely  upon 
the  method  of  making  the  tests.  Natural  cement  is 
usually  somewhat  lighter. 

ART.  38.     SPECIFIC  GRAVITY. 

The  determination  of  specific  gravity  is  often  sub- 
stituted for  that  of  apparent  density,  and  is  a  much 
better  guide  to  a  knowledge  of  the  actual  density  of 
the  material,  as  it  is  not  subject  to  the  fluctuations 
due  to  fineness  or  method  of  determination  which 
characterize  the  weight  tests.  The  differences  of 
specific  gravity  to  be  determined  are,  however,  very 
small,  and  great  care  is  necessary  in  the  manipulation 
of  the  test  in  order  to  obtain  reliable  results. 

The  test  for  specific  gravity  is  commonly  made  by 
immersing  a  known  weight  of  the  cement  in  a  liquid 
which  will  not  act  upon  it,  and  obtaining  its  volume 
through  noting  the  volume  of  liquid  displaced.  In 
making  the  test  by  this  method  it  is  necessary  that 
all  the  air-bubbles  contained  in  the  cement  powder  be 
eliminated,  and  that  the  volume  obtained  be  that  of 
the  cement  particles  only. 

Schumann  Volumenometer. — Several  forms  of  appa- 
ratus have  been  used  for  this  purpose.  Of  these  the 
Schumann  volumenometer,  shown  in  Fig.  5,  is  perhaps 
the  most  common.  It  consists  of  a  graduated  tube, 
the  bottom  of  which  is  ground  to  fit  closely  into  the 
top  of  a  flask. 

In  the  use  of  the  apparatus  the  tube  is  placed  upon 
the  flask  and  filled  with  benzine  to  the  zero-point  on 


METHODS  OF  TESTING  CEMENT. 


97 


the  scale.  100  grammes  of  cement  are  then  weighed 
and  carefully  poured  into  the  top  of  the  tube  so  as  to 
sift  gradually  through  the  liquid,  thus  allowing  the  air 
to  escape. 

The  elevation  of  the  surface  of  the  liquid  in  the  tube 


FIG.  5. 

gives  the  volume  of  the  cement.  The  scale  as  ordi- 
narily made  has  a  range  of  40  cubic  centimeters,  and 
is  graduated  to  i/io  centimeter.  This  volumenometer 
gives  very  satisfactory  results  when  carefully  used,  but 
much  care  is  required  to  fully  eliminate  the  air  and 
prevent  the  powder  from  adhering  to  the  surface  of 
the  tube.  It  is  well  in  operating  in  this  manner  to 


98  HYDRAULIC  CEMENT. 

introduce  the  liquid  through  a  long  funnel,  thus  keep- 
ing the  inner  surface  of  the  tube  dry. 

In  some  instances  greater  accuracy  may  perhaps 
be  obtained  by  filling  the  apparatus  to  the  zero-point 
with  liquid  and  weighing  the  whole,  then  pouring  in 
enough  cement  through  a  funnel  to  raise  the  surface 
of  the  liquid  through  a  definite  volume,  and  determin- 
ing the  weight  of  cement  by  reweighing  the  whole. 
This  eliminates  the  error  due  to  loss  of  cement  powder 
in  introducing  it  into  the  flask. 

Candlof  s  Volumenometer. — M.  Candlot  has  modified 
the  Schumann  volumenometer  by  closing  the  upper 
end  of  the  tube  with  a  glass  bulb.  In  using  this  form 
of  the  apparatus  the  tube  is  turned  bottom  upward 
and  the  bulb  filled  with  benzine.  The  flask  is  then 
placed  upon  the  tube,  the  apparatus  is  inverted,  and  a 
reading  taken  of  the  height  reached  upon  the  tube. 
A  weighed  quantity  of  cement  is  then  placed  in  the 
tube,  which  is  turned  upside  down  and  separated  from 
the  flask  for  the  purpose.  The  flask  being  replaced 
and  the  whole  again  inverted,  the  volume  is  shown  by 
the  use  of  the  liquid  in  the  tube.  In  order  to  elimi- 
nate the  air-bubbles  the  apparatus  is  shaken  before 
taking  the  second  reading  so  as  to  thoroughly  mix  the 
liquid  and  the  cement. 

This  method  is  much  more  rapid  than  that  with  the 
Schumann  volumenometer,  but  in  practice  is  hardly  so 
satisfactory  in  result. 

Le  Chatelier 's  Volumenometer. — This  apparatus  is 
shown  in  Fig.  6.  It  consists  of  a  flask  the  top  of 
which  is  drawn  out  into  a  tube  i  cm.  in  diameter  and 
20  cm.  long.  Above  the  middle  the  tube  enlarges 


-METHODS   OF  TESTING  CEMENT. 


99 


into  a  bulb  for  a  short  space,  and  then  again  continues 
with  uniform  diameter  to  the  top.  The  flask  to  a 
point  marked  on  the  tube  just  below  the  bulb  has  a 
capacity  of  100  cubic  centimeters.  From  this  point 
to  a  mark  above  the  bulb  the  capacity  is  20  cubic 


0 


FIG.  6. 

centimeters.  This  latter  mark  is  very  carefully  deter- 
mined, and  the  upper  part  of  the  tube  is  graduated 
to  1/10  cubic  centimeter. 

In  using  this  apparatus,  the  flask  is  filled  with  liquid 
to  the  mark  below  the  bulb,  and  the  cement  is  then 
slowly  introduced  through  a  funnel,  and  settles  through 
the  liquid  into  the  flask,  the  air  being  eliminated  by 


IOO  HYDRAULIC   CEMENT. 

its  long  passage  through  the  liquid.  Cement  is 
added  until  the  surface  of  the  liquid  rises  to  the  20- 
cubic-centimeter  mark.  The  weight  of  this  volume 
of  cement  is  obtained  by  weighing  the  apparatus  before 
and  after  the  cement  is  introduced.  Or,  this  volu- 
menojneter  may  be  used  in  the  same  manner  as  that 
of  Dr.  Schumann,  the  bulb  serving  to  prevent  the 
cement  sticking  to  the  sides  of  the  tube. 

Mann  Gravimeter. — This  apparatus  consists  of  a 
flask  which  when  filled  to  a  certain  mark  upon  its  neck 
contains  an  accurately  known  quantity  of  liquid.  A 
graduated  tube  with  a  stop-cock  at  its  lower  end  con- 
tains when  full  the  same  quantity  as  the  flask. 

A  weighed  quantity  of  cement  is  placed  in  the  flask 
and  the  tube  is  filled  with  the  liquid  to  be  used.  The 
liquid  is  then  allowed  to  run  from  the  tube  into  the 
flask,  reliance  being  placed  upon  shaking  the  flask  to 
eliminate  air-bubbles,  until  the  flask  is  filled  to  the 
volume  mark.  The  volume  of  liquid  remaining  in  the 
graduated  tube  is  then  equal  to  the  volume  of  cement 
powder.  The  complete  eradication  of  the  air  is  a 
matter  of  difficulty,  and  if  the  operation  is  conducted 
altogether  in  the  air  the  change  of  temperature  may 
be  sufficient  to  affect  the  result.  This  method  in 
practice  is  not  likely  to  give  very  concordant  results. 

Erdmenger* s  Volumenometer  is  a  modification  of  the 
Mann  apparatus,  looking  to  the  maintenance  of  a  con- 
stant temperature  during  the  test.  This  arrangement 
is  shown  in  Fig.  7.  It  consists  of  a  graduated  tube 
of  50  cubic  centimeters  capacity,  partially  enclosed  in 
a  larger  vessel  which  acts  as  a  cooler.  The  upper  end 
of  the  tube  is  closed  with  a  ground-glass  stopper,  the 


METHODS   OF   TESTING  CEMENT. 


101 


lower  end  with  a  stop-cock.  Near  its  lower  end  the 
tube  has  a  horizontal  branch,  also  closed  by  a  cock, 
and  connecting  it  with  a  jar  of  I  liter  capacity  having 
two  openings  at  the  top,  one  being  connected  with  the 
measuring  tube,  the  other  with  a  rubber  pressure-ball. 
The  cooler  has  two  openings  at  the  top,  one  of  which 
serves  to  permit  the  passage  of  air,  the  other  to  admit 
a  small  thermometer.  To  fill  the  cooler  with  water, 


DDfl 


FIG.  7. 

or  empty  it,  an  opening  is  placed  at  the  bottom  which 
may  be  controlled  by  a  stop-cock.  A  narrow-necked 
flask  of  the  capacity  of  50  cubic  centimeters  is  used  for 
the  measurement  of  the  volume  of  the  cement. 

In  making  the  test  the  apparatus  is  kept  at  a  tem- 
perature of  about  60°  Fahr.  by  filling  the  cooler  with 
water  at  that  temperature  and  standing  the  double- 
necked  jar  containing  the  liquid  to  be  used  in  the  test 
and  the  measuring-flask  in  vessels  of  water  of  the  same 
temperature.  The  measuring-flask  is  then  filled  to 


102  HYDRAULIC   CEMENT. 

the  5o-cubic-centimeter  mark  with  the  fluid,  and  the 
test  is  made  as  with  the  Mann  apparatus;  or  the  mix- 
ing of  the  liquid  with  the  cement  may  be  done  by 
putting  the  cement  in  a  small  funnel,  and  washing  it 
through  with  the  liquid,  thus  eliminating  the  air. 

Any  of  these  volumenometers  may  give  good  results 
when  carefully  handled,  the  Schumann  and  Le  Chate- 
lier  forms  being  easiest  to  handle  satisfactorily. 

Benzine  or  turpentine  is  usually  employed  as  the 
fluid,  and  it  is  important  that  the  liquid  should  be 
maintained  at  a  nearly  uniform  temperature  during 
the  test.  For  this  reason  it  is  common  to  immerse 
the  apparatus  in  cool  water.  Where  benzine  is  used 
the  temperature  should  not  rise  above  60°  Fahr.  It 
is  desirable  also  to  sift  the  cement  to  be  tested  through 
a  fine  sieve,  on  account  of  the  better  elimination  of 
air-bubbles  possible  with  the  fine  material. 

In  order  to  make  the  determination  of  specific 
gravity  of  value,  it  must  be  reliable  to  two  decimal 
places.  Portland  cement  varies  from  about  3.00  to 
3. 18,  and  is  usually  above  3.05.  Natural  cements  vary 
from  2.75  to  3.05.  An  inferior  limit  is  sometimes 
fixed  in  specifications — usually  for  Portland  cement 
about  3.00  or  3.05,  and  for  Roman  cement  about  2.80. 

The  presence  of  the  volatile  elements  due  to  incom- 
plete burning,  or  of  adulterations  added  after  the 
burning,  tends  to  lower  the  specific  gravity.  The 
quantity  of  adulteration,  however,  needs  to  be  con- 
siderable before  it  becomes  appreciable  in  the  results 
of  this  test. 

The  specific  gravity,  unlike  the  apparent  density,  is 
not  affected  by  the  fineness  of  grinding;  and  it  has 


METHODS   OF  TESTING   CEMENT.  103 

been  suggested  by  examination  of  the  results  of  cer- 
tain experiments  that  a  comparison  of  the  two  tests 
for  the  same  material  may  sometimes  give  a  better 
determination  of  the  actual  fineness  than  can  be 
obtained  by  the  use  of  sieves.  This  fineness  is  shown 
practically  by  the  greater  ability  of  the  fine  cement  to 
"  take  sand  "  without  losing  in  early  strength. 

ART.  39.     TESTS  FOR  FINENESS. 

The  fineness  to  which  a  cement  is  ground  is  usually 
considered  a  matter  of  importance,  as  upon  it  depends 
very  greatly  the  early  adhesive  strength  of  the  mortar 
and  the  ability  of  the  cement  to  take  sand. 

A  test  for  fineness  is  nearly  always  included  in 
specifications  for  cement,  and  the  test  is  particularly 
necessary  where  the  tensile  strength  is  tested  for  neat 
cement  only.  In  such  case  the  attainment  of  a  proper 
strength  neat,  together  with  a  fair  degree  of  fineness, 
practically  insures  that  the  cement  will  give  good 
results  when  used  with  sand. 

The  fineness  which  should  be  required  is  largely  a 
matter  of  relative  economy;  the  finer  the  cement,  the 
larger  the  quantity  of  sand  that  may  legitimately  be 
used  with  it.  The  coarse  parts  of  the  cement  are  to 
be  considered  as  inert  material,  or  practically  as  a 
certain  amount  of  sand  already  mixed  with  the  cement. 
It  is  a  question  therefore  of  relative  costs  of  different 
degrees  of  fineness. 

There  is,  however,  some  dispute  as  to  the  value  of 
fineness.  Some  European  authorities  question  the 
wisdom  of  a  fineness  test.  It  is  well  known  that  the 


IO4  HYDRAULIC   CEMENT. 

effect  of  fineness  in  the  strength  of  sand-mortar  dis- 
appears to  some  extent  with  time,  but  the  impalpable 
powder  seems  to  be  the  really  valuable  part  of  the 
cement,  and  if  this  be  omitted  the  cement  loses  its 
value. 

Prof.  Le  Chatelier  in  his  microscopic  examination 
of  mortar  found  that,  after  setting,  in  the  more  fine 
particles  no  trace  is  left  of  the  grains  of  the  cement. 
With  the  larger  ones  the  central  part  of  the  grain 
remains  unaltered.  It  seems  that  the  grains  which 
are  completely  attacked  are  limited  to  o.  I  millimeter 
in  diameter,  but. further  study  is  needed  upon  this 
point. 

Coarse  grinding  also,  as  has  been  elsewhere  noted, 
increases  the  intensity  of  the  action  of  expansives 
which  may  be  contained  in  the  cement,  causing  a 
coarse-ground  cement  to  expand  and  crack,  when  per- 
haps if  finely  ground  it  would  be  unaffected. 

The  test  for  fineness  simply  consists  in  sifting  the 
cement  through  a  sieve  or  a  set  of  sieves,  and  observ- 
ing the  amount  retained  by  each  sieve. 

The  committee  of  the  American  Society  of  Civil 
Engineers  upon  "  standard  tests"  recommend  the  use 
of  sieves  of  2500,  54/6,  and  10,000  meshes  per  square 
inch.  Specifications  usually,  however,  require  only  a 
single  sieve — generally  that  of  2500  meshes,  but  some- 
times that  of  10,000  meshes.  A  more  general  use  of 
the  finer  sieve  would  undoubtedly  be  advantageous, 
as  it  is  now  generally  admitted  that  all  material  coarser 
than  that  dimension  is  practically  inert,  and  a  real 
measure  of  useful  fineness  is  not  given  by  the  21500- 
mesh  sieve  A  common  requirement  is  that  not  more 


METHODS   OF  TESTING   CEMENT.  10$ 

than  io#  by  weight  of  the  cement  be  retained  upon  a 
sieve  of  2500  meshes,  or  that  not  more  than  20$  be 
retained  upon  that  of  10,000  meshes,  or  both.  Most 
of  the  cements  commonly  in  use  in  the  United  States 
easily  comply  with  these  requirements.  Very  many 
of  them  do  not  give  a  residue  on  the  coarse  sieve  of 
more  than  i#  to  3$,  or  on  the  fine  one  of  more  than 
8#  to  io#.  Some  cements,  however,  seem  to  be 
bolted  with  special  reference  to  passing  the  test  of  the 
25OO-mesh  sieve,  and  are  very  coarse  when  tested  with 
a  finer  one. 

The  sizes  of  wire  of  which  the  sieves  are  made  is  of 
course  important  as  regulating  the  sizes  of  the  open- 
ings, and  should  always  be  stated ;  the  common  stand- 
ard is  that  the  diameter  of  wire  should  be  about  1/3 
of  the  spacing  between  centres..  The  sieves  of  the 
American  Society  of  Civil  Engineers  mentioned  above 
are  of  Nos.  35,  37,  and  40  wire-gauge. 

It  is  not  usually  practicable  to  get  sieves  with  per- 
fect regularity  either  of  spacing  or  diameter  of  wires. 
A  sufficiently  near  approximation  for  practical  work 
may  be  obtained  by  using  care  in  selecting  the  sieve, 
but  the  gauge  frequently  offered  for  this  use  differs 
very  considerably  in  the  sizes  of  openings  for  the  same 
number  per  inch,  and  sometimes  the  openings  are 
quite  irregular  in  size  in  different  parts  of  the  same 
sieve. 

ART.  40.     RATE  OF  SETTING. 

The  rate  of  setting  of  cement  is  tested  for  the  pur- 
pose of  determining  if  it  be  suitable  for  a  given  use, 


106  HYDRAULIC   CEMENT. 

and  not  as  a  measure  of  the  quality  of  the  material. 
For  most  purposes,  where  immediate  setting  is  not 
required  to  prevent  disturbance  of  the  mortar  before 
hardening,  the  moderately  slow-setting  cements  are 
found  most  convenient,  as  they  need  not  be  handled 
so  quickly,  and  may  be  mixed  in  somewhat  larger 
uantities. 

Testing  for  time  of  setting  consists  in  arbitrarily 
fixing  two  points  in  the  process  of  consolidation, 
which  are  called  the  beginning  and  the  end  of  setting. 
These  points  are  differently  determined  in  the  vari- 
ous methods  of  testing,  and  are  not  marked  by  any 
distinguishing  phenomena  which  admit  of  definite 
determination. 

The  method  recommended  by  the  committee  of  the 
American  Society  of  Civil  Engineers  is  that  proposed 
by  General  Gillmore,  and  consists  in  mixing  cakes  of 
neat  cement,  about  2  or  3  inches  in  diameter  and  1/2 
inch  thick,  to  a  stiff  plastic  consistency,  observing  the 
time  when  they  will  _bear_.  a  needle  1/12  inch  in 
diameter  sustaining  a  weight  of  1/4  pound,  and  noting 
this  as  the  beginning  of  setting;  then  continuing  the 
observations  with  a  needle  1/24  inch  in  diameter 
carrying  a  weight  of  one  pound  until  the  material  is 
sufficiently  firm  to  bear  this,  when  it  may  be  called 
fully  set.  The  committee  call  those  cements  which 
set  in  1/2  hour  or  less,  quick-setting;  those  requiring 
x.  more  time,  slow-setting. 

The  time  of  setting  is  often  roughly  determined  in 
practice  by  making  small  cakes  of  mortar  and  observ- 
ing when  they  will  resist  penetration  under  a  light 


METHODS   OF  TESTING   CEMENT.  IO7 

pressure  of  the  thumb-nail.  This  is  a  standard  test  in 
Germany. 

For  ordinary  practical  purposes  these  methods  are 
sufficiently  accurate,  as  all  that  is  necessary  is  to  know 
whether  the  cement  sets  quickly  or  slowly,  but  for 
experimental  and  comparative  purposes  more  elaborate 
methods  are  valuable.  The  beginning  of  setting  is  the 
point  of  most  value,  as  the  cement  in  practice  should 
be  used  before  that  point  is  reached,  in  order  that  it 
may  not  be  disturbed  after  the  stiffening  has  begun. 

In  Germany  and  France  the  Vicat  needle  is  com- 
monly employed  for  accurate  determinations.  This 
arrangement  is  shown  in  Fig.  8.  By  this  method  a 


FIG.  8. 


briquette  of  neat  cement  is  made  in  a  cylindrical  brass 
or  rubber  mould  10  centimeters  in  diameter  and  4 
centimeters  high,  placed  upon  a  plate  of  glass  or 
metal,  the  cement  being  mixed  to  a  plastic  consist- 


108  HYDRAULIC   CEMENT. 

ency  as  determined  by  the  consistency  test.  The 
apparatus  is  so  arranged  that  a  weight  of  300  grammes 
may  be  brought  either  upon  a  needle  of  I  square  mil- 
limeter section,  or  upon  a  cylindrical  plunger  I  centi- 
meter in  diameter,  and  allowed  to  settle  into  the 
cement,  the  depth  of  penetration  being  shown  by  a 
scale  along  which  the  weight  slides.  As  soon  as  the 
mould  is  filled  with  the  mortar  it  is  placed  in  the 
apparatus,  and  the  plunger,  sustaining  the  300 
grammes,  is  brought  to  the  surface  of  the  briquette 
and  allowed  to  sink  into  it.  If  the  plunger  penetrates 
to  a  point  6  millimeters  from  the  bottom  the  mortar 
is  of  proper  consistency  for  the  test.  The  needle  is 
then  substituted  for  the  plunger,  and  the  time  when 
the  needle  first  refuses  to  sink  entirely  through  the 
mortar  is  observed  and  noted  as  the  beginning  of  set- 
ting; the  time  when  the  needle  first  rests  upon  the 
briquette  without  penetrating  it  is  considered  the  end 
of  setting. 

The  accurate  determination  by  this  method  of  the 
points  where  the  set  is  said  to  begin  and  end  is  a 
matter  of  some  difficulty,  as  the  lack  of  perfect  homo- 
geneity causes  the  needle  to  sink  more  deeply  in  some 
parts  than  in  others,  and  the  cement  sets  more  rapidly 
at  the  circumference  than  in  the  interior  of  the  mass. 
However,  these  defects  are  not  very  serious  when  due 
care  is  exercised  in  mixing  the  mortar,  and  the  pene- 
tration is  not  taken  too  near  the  edges.  The  time  of 
completion  of  set  is  much  less  well  defined  than  that 
of  beginning  of  set,  as  there  is  usually  a  considerable 
period  during  which  a  very  slight  penetration  takes 
place,  decreasing  insensibly  to  final  disappearance. 


METHODS   OF  TESTING   CEMENT.  109 

The  point  to  be  used  for  completion  of  the  set  is  that 
at  which  the  penetration  becomes  very  small,  so  that 
the  curve  of  penetrations  becomes  practically  horizon- 
tal. Such  a  point  is  usually  fairly  well  defined. 

Various  modifications  of  this  method  have  been  pro- 
posed for  the  purpose  of  securing  greater  uniformity 
in  result,  but  they  have  not  come  into  general  use. 
M.  Bonnami  has  proposed  to  modify  the  test  by  vary- 
ing the  weight  upon  the  needle  instead  of  the  depth 
of  penetration.  He  measures  the  time  at  which 
various  weights  will  cause  the  penetration  of  the  needle 
to  mid-depth  in  the  mortar,  beginning  with  50  grammes 
which  marks  the  beginning  of  setting,  and  increasing 
to  3000  grammes,  which  gives  the  end  of  setting,  thus 
obtaining  a  curve  of  times  in  terms  of  weights  sus- 
tained. The  penetration  to  mid-depth  is  selected  as 
the  point  of  maximum  variation. 

The  time  of  setting  is  usually  tested  upon  paste  of 
neat  cement,  on  account  of  the  difficulty  of  obtaining  a 
satisfactory  test  with  sand-mortar.  The  Vicat  needle 
is  quite  useless  when  sand  is  employed  because  of  the 
interference  of  the  grains  of  sand  with  the  descent  of 
the  needle.  Rough  tests  of  sand-mortar  by  the 
ordinary  methods  may  readily  be  made  with  sufficient 
accuracy  for  practical  purposes,  and  are  very  desirable 
as  showing  more  nearly  what  may  be  expected  of  the 
mortar  when  used.  The  rate  of  setting  of  neat  mortar 
gives  but  little  indication  of  what  the  action  may  be 
with  sand.  For  different  cements  a  mortar  of  3  parts 
sand  to  I  of  cement  may  require  from  about  i£  to  8 
or  10  times  as  long  as  neat  paste  when  the  same  sand 
and  method  of  mixing  are  employed. 


I  10  HYDRAULIC   CEMENT. 

Several  propositions  have  been  made  with  reference 
to  a  standard  test  for  the  purpose  of  comparing  the 
rate  of  setting  of  sand-mortars.  These  usually  have 
been  to  substitute  cylinders  of  larger  diameter  for  the 
Vicat  needle,  in  order  to  reduce  the  effect  of  the  sand 
grains,  and  then  to  use  correspondingly  heavy  weights 
to  produce  penetration.  The  usual  method  is  to 
determine  the  weight  necessary  to  indent  the  surface 
of  the  mortar.  Thus  in  one  apparatus  a  cylinder  I 
cm.  in  diameter  is  employed:  when  the  mortar  will 
just  bear  a  weight  of  400  grammes  it  is  considered  as 
beginning  to  set;  when  it  will  sustain  10,000  grammes 
the  setting  is  complete. 

M.  Feret  has  also  proposed  to  make  standard  tests 
by  using  fine  sand  composed  of  grains  which  pass  the 
sieve  of  75  meshes  and  are  held  by  one  of  180  meshes 
per  linear  inch,  the  test  being  made  as  for  neat 
cement  with  the  Vicat  needle.  This  serves  as  a  com- 
parison of  the  effects  of  sand  upon  different  cements. 

In  making  tests  for  rate  of  setting,  the  temperature 
of  the  ingredients  of  the  mortar  before  gauging,  that 
of  the  atmosphere  in  which  it  is  gauged,  and  of  the  air 
or  water  in  which  it  is  placed  during  setting  have  a 
very  large  influence  upon  the  results.  A  temperature 
of  60°  to  65°  Fahr.  is  usually  accepted  as  standard, 
although  the  air  in  the  laboratory  may  have  a  some- 
what higher  temperature — perhaps  65°  to  70°. 

The  amount  of  water  used  in  gauging  and  the 
methods  of  mixing  the  mortar  and  filling  the  mould 
are  important.  For  the  purpose  of  regulating  these, 
the  consistency  of  the  mortar  is  prescribed.  This  is 
probably  the  best  means  of  arriving  at  uniform  results, 


METHODS  OF  TESTING  CEMENT.  in 

but  it  should  be  pointed  out  that  the  same  consistency 
may  be  arrived  at  in  two  ways — by  using  a  small 
quantity  of  water  and  working  thoroughly,  or  by  using 
a  larger  quantity  and  working  less.  The  quantity  of 
water  which  will  bring  the  mortar  to  proper  consistency 
after  three  or  four  minutes  of  vigorous  working  is  the 
most  desirable,  but  there  is  opportunity  for  consider- 
able variation  in  the  results  of  the  test  as  carried  out 
by  different  operators. 

A  number  of  automatic  appliances  have  been  devised 
for  the  purpose  of  making  these  tests  without  constant 
attendance.  That  of  Professor  Fuertes,  in  the  labora- 
tory of  the  College  of  Civil  Engineering,  Cornell  Uni- 
versity, consists  of  a  trough  i£  inches  wide  by  2£ 
inches  deep,  in  which  the  mortar  is  placed.  A  car  is 
drawn  along  a  track  over  the  trough  by  means  of  a 
screw  rotated  by  a  clock,  thus  giving  a  motion  vary- 
ing uniformly  with  time.  From  the  car  is  suspended 
a  Vicat  needle,  which  is  dropped  and  raised  at  regular 
intervals  by  the  action  of  a  small  stream  of  water.  A 
pencil  attached  to  the  shaft  of  the  needle  draws  the 
curve  of  penetrations  upon  a  board  at  the  side  of  the 
trough. 

ART.  41.     CHANGE  OF  TEMPERATURE  DURING 
SETTING. 

Observations  of  the  change  of  temperature  during 
setting  are  commonly  taken  in  many  of  the  European 
laboratories.  It  has  been  thought  by  some  observers 
that  the  points  of  beginning  and  end  of  setting  might 
be  more  accurately  marked  by  observing  the  change 
of  temperature  than  by  the  needle  test.  The  opera- 
tion of  setting  is  a  chemical  action  which  takes  place 


112  HYDRAULIC  CEMENT. 

with  the  disengagement  of  heat,  but  in  many  cases 
the  rise  in  temperature  is  so  slight  and  indefinitely 
marked  that  it  would  be  difficult  to  use  it  in  this 
manner.  The  amount  of  the  variation  in  tempera- 
ture varies  somewhat  with  the  activity  of  the  cement, 
increasing  rapidly  as  the  cement  sets  more  quickly. 
The  total  rise  of  a  quick-setting  cement  may  reach  15° 
or  20°,  while  in  a  very  slow  one  it  may  be  quite  im- 
perceptible. 

The  change  in  temperature  also  varies  with  the 
nature  of  the  cement,  and  attempts  have  been  made 
to  connect  it  with  the  soundness  of  the  material,  par- 
ticularly the  presence  of  free  lime.  This,  however, 
does  not  seem  to  be  supported  by  facts,  or  at  least 
the  indications  are  very  indefinite.  Expansives  which 
are  slow  in  action,  and  therefore  dangerous  in  the 
cement,  are  not  likely  to  cause  increase  in  temperature 
during  setting. 

The  test  for  change  in  temperature  is  ordinarily 
made  by  placing  the  mortar  in  a  cylindrical  mould, 
like  that  used  with  the  Vicat  needle,  fitted  with  a 
cover  through  which  is  an  opening  to  permit  the  intro- 
duction of  the  thermometer.  This  cover  prevents  the 
mortar  coming  into  contact  with  the  air  or  water  in 
which  it  may  be  placed,  thus  neutralizing  the  effect 
of  the  internal  change  of  temperature. 

Some  very  slow-setting  cements  show  a  fall  in  tem- 
perature if  left  exposed  to  the  air  while  setting,  prob- 
ably due  to  surface  evaporation. 

This  test  does  not  seem  of  importance  as  a  measure 
of  the  quality  of  cement,  but  it  is  worthy  of  attention 
in  a  systematic  study  of  the  properties  of  the  material, 
and  may  be  capable  of  giving  interesting  results. 


CHAPTER   VI. 
TESTS   OF  THE   STRENGTH   OF   MORTAR. 

ART.  42.     METHODS  EMPLOYED. 

THE  strength  of  mortar  is  frequently  tested  in  three 
ways:  the  tensile  test  is  the  one  more  commonly  em- 
ployed, but  compressive  and  transverse  tests  are  also 
often  used. 

The  test  for  tensile  strength  is  made  by  making 
briquettes  of  the  mortar  in  moulds  having  a  definite 
section  at  the  middle, — in  the  United  States  usually 
one  inch  square, — and  enlarging  at  the  ends  to  fit 
in  clips  by  which  they  may  be  placed  in  the  testing- 
machine  and  pulled  apart  by  direct  tension.  This 
test  is  in  common  use,  because  it  can  be  more  readily 
and  uniformly  applied  than  the  others,  and  seems, 
when  coupled  with  other  tests,  to  give  a  satisfactory 
indication  of  the  value  of  the  material. 

The  compressive  test  consists  in  crushing  small 
blocks  of  the  mortar  between  the  jaws  of  the  testing- 
machine  and  weighing  the  force  required.  This  test 
is  more  difficult  in  manipulation  to  secure  uniform 
results,  and  also  requires  much  heavier  appliances,  on 
account  of  the  high  resistance  offered  by  the  material 
to  crushing. 

"3 


114  HYDRAULIC   CEMENT. 

The  transverse  test  is  made  by  moulding  the  mortar 
into  bars;  the  bar  is  afterward  placed  horizontally 
upon  supports  near  its  ends,  and  broken  by  a  load 
brought  upon  its  middle,  causing  it  to  break  by  bend- 
ing. 

The  proper  conduct  of  any  test  for  strength  is  a 
matter  requiring  care  and  experience.  There  are 
many  points  connected  with  the  circumstances  and 
manipulation  of  the  work  which  have  an  important 
bearing  upon  the  result.  These  are:  the  form  of  the 
briquette;  the  method  of  mixing  and  moulding;  the 
amount  of  water  used  in  tempering  the  mortar;  the 
surroundings  in  which  the  mortar  is  kept  during  the 
hardening;  the  rate  and  manner  of  applying  the  stress; 
the  temperature  at  which  all  of  the  operations  are 
performed.  In  order  to  secure  uniform  results  it  is 
essential  that  the  tests  be  standardized  in  all  of  these 
particulars.  Much  has  been  accomplished  in  this 
direction  during  recent  years,  but  there  is  still  great 
disparity  in  the  results  of  different  operators,  un- 
doubtedly due  mainly  to  differences  in  making  the 
briquettes. 

Every  laboratory  seems  to  have  to  a  certain  extent 
its  own  practice,  which  makes  its  work  incomparable 
with  that  of  any  other  laboratory.  Even  where  pre- 
sumably the  same  methods  are  used  it  is  very  difficult 
to  frame  rules  that  all  will  understand  alike,  while  in 
all  cases  the  personal  equation  of  the  operator  is  an 
important  matter  in  hand-work. 

The  committee  upon  standard  tests  of  the  American 
Society  of  Civil  Engineers  in  their  report  call  attention 
to  this  matter  in  the  following  words: 


TESTS   OF  THE   STRENGTH    OF   MORTAR.          115 

"  The  testing  of  cement  is  not  so  simple  a  process 
as  it  is  sometimes  thought  to  be.  No  small  degree  of 
experience  is  necessary  before  one  can  manipulate  the 
materials  so  as  to  obtain  even  approximately  accurate 
results. 

"  The  first  tests  of  inexperienced  though  intelligent 
and  careful  persons  are  usually  very  contradictory 
and  inaccurate,  and  no  amount  of  experience  can 
eliminate  the  variations  introduced  by  the  personal 
equation  of  the  most  conscientious  observers.  Many 
things,  apparently  of  minor  importance,  exert  such  a 
marked  influence  upon  the  results,  that  it  is  only  by 
the  greatest  care  in  every  particular,  aided  by  experi- 
ence and  intelligence,  that  trustworthy  tests  can  be 
made." 

Experience,  since  the  report  of  the  committee  was 
made,  has  shown  that  the  difficulties  in  the  way  of 
uniformity  in  such  tests  are  much  greater  than  was 
then  imagined. 

The  variations  in  the  results  of  the  tensile  test 
between  the  work  of  different  experienced  operators 
working  by  the  same  method  and  upon  the  same  ma- 
terial are  frequently  very  large,  and  often  make  all  the 
difference  between  the  acceptance  and  rejection  of  the 
cement.  Differences  of  40$  to  60%  with  neat  cement 
are  not  uncommon,  while  for  sand-mortar  they  are 
much  greater. 

An  investigation  of  this  matter  by  Prof.  J.  M. 
Porter,  of  Lafayette  College,  is  interesting  in  this 
connection.  He  divided  a  sample  of  cement  into  a 
number  of  parts,  sending  each  to  a  different  laboratory 
with  the  request  that  tests  be  made  of  it  in  I  to  3 


Il6  HYDRAULIC   CEMENT. 

mortar,  according  to  the  rules  recommended  by  the 
committee  of  the  American  Society  of  Civil  Engineers. 
The  resulting  average  strengths  of  each  of  the  nine 
laboratories  were  as  follows,  in  pounds  per  square 
inch:  75,  102,  114,  133  and  140,  153,  163,  176,  225, 
247.  These  results  (see  Engineering  News,  March  5, 
1896)  show  that  the  lowest  strength  was  but  30$  of 
the  highest,  while  the  remainder  were  quite  evenly 
distributed  between  the  two  extremes.  Each  result 
was  the  average  of  five  briquettes,  which  agree  fairly 
well  among  themselves. 

If  the  results  of  experienced  men  in  the  permanent 
laboratories  vary  so  much,  what  is  to  be  expected  of 
tests  made  by  less  experienced  men  for  the  reception 
of  material  upon  temporary  work,  and  how  can  a 
specification  be  framed  which  shall  fairly  determine 
the  value  of  the  material?  Evidently,  to  secure  proper 
results  with  hand-work,  the  inspector  must  first  be 
calibrated,  and  the  specifications  drawn  in  accordance 
with  the  practice  of  the  laboratory.  It  is  at  least  very 
desirable  that  some  means  be  devised  by  which  the 
work  of  these  tests  may  be  made  automatically,  and 
the  personal  factor  eliminated  in  so  far  as  possible. 

In  standard  tests  it  is  customary  to  adopt  a  nearly 
constant  temperature  of  60°  to  65°  Fahr.  for  the  air 
in  the  laboratory  in  which  the  briquettes  are  prepared 
and  the  tests  made,  and  about  the  same  or  slightly 
less  for  the  water  used  in  tempering  and  that  in  which 
the  mortar  is  immersed  during  hardening. 


TESTS   OF  THE   STRENGTH   OF   MORTAR. 


ART.  43.     FORM  OF  BRIQUETTE. 

Briquettes  of  mortar  for  tests  of  strength  are  com- 
monly formed  in  moulds  of  metal  of  the  form  to  be 
used  in  the  tests.  As  the  size  and  shape  of  the  speci- 
mens have  an  important  effect  upon  the  result,  it  is 
necessary  to  adopt  standard  dimensions  in  order  to 
obtain  uniform  results. 

For  compressive  tests  a  parallelepiped,  usually  a 
cube,  is  employed.  In  the  United  States  a  cube 
whose  edges  are  each  two  inches  in  length  is  com- 
monly used,  although  sometimes  an  inch  cube  is  used. 
In  Europe  generally  the  standard  specimen  is  a  cube 
with  edges  seven  centimeters  in  length. 

The  French  "  Commission  upon  Methods  of  Testing 
Materials,"  however,  rejected  the  rectangular  section 
for  compression  specimens  on  the  ground  that  it  is 
difficult  to  so  fill  the  corners  of  the  moulds  as  to  make 
homogeneous  briquettes,  and  they  recommend  the 
cylindrical  form  as  preferable.  They  also  recommend 
the  use  of  half-briquettes  obtained  by  the  tension  test 
as  blocks  for  the  crushing  test. 

For  transverse  tests  bars  of  rectangular  section  are 
used.  Different  experimenters  have  used  quite  differ- 
ent dimensions,  and  there  is  no  size  which  may  reason- 
ably be  called  a  standard.  Those  who  have  proposed 
the  adoption  of  this  test  in  place  of  that  for  tension  in 
the  acceptance  of  material  have  usually  advocated  a 
test-piece  of  a  section  one  inch  square  and  from  eight 
to  twelve  inches  long,  although  sometimes  the  section 
is  made  two  inches  square. 


HYDRAULIC   CEMENT. 


For  tensile  tests  many  forms  of  briquettes  have 
been  tried,  but  at  present  there  are  but:  two  in  com- 
mon use:  the  one  recommended  by  the  committee  of 
the  American  Society  of  Civil  Engineers  (shown  in 
Fig.  9),  which  was  derived  from  that  used  by  Mr. 
Grant  in  England,  is  now  the  standard  in  the  United 
States,  and  commonly  used  in  England;  the  other  is 
the  form  adopted  by  the  Association  of  German 


FIG.  9. 


FIG    10. 


Cement  Makers,  and  is  the  standard  in  Germany,  and 
generally  employed  in  France.  This  form  is  shown 
in  Fig.  10,  which  gives  the  dimensions  in  millimeters. 
The  middle  section  is  22.5  mm.  wide  by  22.2  mm. 
thick,  giving  a  cross-section  of  5  square  centimeters. 

Comparative  tests  of  briquettes  of  the  two  forms 
indicate  that  the  English  form  gives  higher  results 
than  the  German,  the  difference  being  commonly  for 
neat  briquettes  as  much  as  30$  to  40$  of  the  smaller. 
This  may  perhaps  be  accounted  for  by  the  fact,  stated 
by  Mr.  Faija,  that  a  sudden  change  of  cross-section  is 
always  an  element  of  weakness,  and  while  the  English 


TESTS   OF  THE   STRENGTH   OF   MORTAR.          I  19 

form  diminishes  gradually  from  the  ends  to  the  middle, 
in  the  German  form  the  area  is  suddenly  decreased  by 
a  circular  notch  at  the  middle. 

It  may  also  be  noted  that  the  surface  upon  which 
the  clip  catches  the  briquette  when  being  tested  is  in 
the  German  form  inclined  at  a  greater  angle  to  the 
centre  line  of  the  briquette,  and  consequently  the 
adjustment  in  the  clips  to  produce  axial  stress  is  less 
perfect. 

In  England  and  the  United  States  the  standard 
area  for  the  middle  is  one  square  inch;  in  Germany 
and  France  a  little  smaller,  being,  as  already  noted, 
five  square  centimeters.  The  use  of  these  small  sec- 
tions is  advantageous,  as  it  admits  of  lighter  apparatus 
in  making  the  test,  and  because  greater  uniformity  is 
easily  attainable  in  making  the  briquette.  The  work 
also  is  facilitated  by  the  fact  that  less  mortar  is 
required  for  each  specimen  than  with  larger  sections, 
so  that  more  briauettes  may  be  prepared  from  each 
mixing. 

The  size  of  the  breaking  section  has  an  important 
effect  upon  the  strength,  the  smaller  sections  giving 
much  higher  strength  per  unit  of  area  than  the  larger 
ones.  Thus  for  neat  cement  a  change  from  a  section 
i  inch  square  to  one  2  inches  square  has  been  found 
to  lessen  the  tensile  strength  per  square  inch  to  about 
one  half  that  of  the  smaller  section.  M.  Durand- 
Claye  has  shown  that  the  strength  varies  more  nearly 
with  the  perimeter  of  the  section  than  with  its  area, 
and  that  the  interior  may  be  removed  without  loss  of 
strength. 

M.  Alexandre  made  a  number  of  experiments  upon 


I2O  HYDRAULIC   CEMENT. 

the  relative  strengths  of  briquettes  of  different  sizes.* 
He  found  that  large  briquettes  gave  much  less  strength 
per  unit  area  than  small  ones,  but  for  sand-mortars 
the  effect  diminished  as  the  proportion  of  sand  in- 
creased, and  the  difference  also  became  less  as  the 
age  of  the  mortar  increased,  seeming  to  indicate  that 
the  effect  may  be  partly  due  to  the  more  perfect 
hardening  of  the  small  specimens 

ART.  44.     QUANTITY  OF  WATER  USED  IN  GAUGING. 

The  determination  of  the  proper  consistency  for 
mortar  is  very  important  in  its  effect  upon  the  results 
of  tests  of  strength.  The  effects  upon  setting  and 
hardening  of  varying  the  quantity  of  water  used  in 
mixing  have  already  been  discussed,  Art.  24. 

In  making  standard  tests  it  is  common  to  regulate 
the  quantity  of  water  by  trying  to  bring  the  mortar 
to  a  normal  consistency  which  shall  be  uniform  for  all 
tests.  Different  cements  require  very  different  quan- 
tities of  water  to  reach  the  same  consistency,  and  in 
the  use  of  sand-mortar  the  nature  and  condition  of 
the  sand  may  also  cause  considerable  variation.  It 
should  also  be  noted  that  the  consistency  of  mortar 
does  not  depend  altogether  upon  the  quantity  of  water 
used,  but  may  be  varied  by  the  manner  and  extent  of 
working  the  mortar  during  the  gaugings.  In  French 
and  German  practice  it  is  required  that  the  mortar  be 
vigorously  worked  for  five  minutes. 

Under  the  different  systems  of  making  briquettes 
there  are  two  consistencies  employed  as  standards — 

*  Annales  des  Fonts  et  Chaussees,  1890,  vol.  n.  p.  277. 


TESTS   OF  THE   STRENGTH   OF   MORTAR.          12! 

the  plastic  and  the  dry.  In  using  each  of  these  meth- 
ods the  quantity  of  water  used  and  the  consistency 
reached  vary  greatly  in  different  places,  as  the  man 
doing  the  work  may  interpret  the  terms  used  in  describ- 
ing the  desired  state  of  the  mortar. 

The  rules  recommended  by  the  committee  of  the 
American  Society  of  Civil  Engineers  describes  the 
condition  of  the  mortar  to  be  used  as  "  stiff  and  plas- 
tic," thus  leaving  much  to  individual  judgment. 

In  Europe  two  methods  are  employed  for  determin- 
ing the  proper  consistency  of  plastic  mortar.  The 
Tetmajer  method  consists  in  determining  the  normal 
consistency  by  the  method  already  described  for  find- 
ing the  time  of  setting  by  the  Vicat  needle  (Art.  40). 
This  method  was  recommended  by  the  conference  of 
German,  Austrian,  Swiss,  and  Russian  engineers  at 
Dresden,  and  also  by  the  French  commission. 

The  Boulogne  method  is  commonly  used  in  France, 
and  also  approved  by  the  French  commission.  It  is 
as  follows: 

The  mortar  is  to  be  vigorously  worked  for  five 
minutes  to  bring  it  to  the  required  consistency. 

"  i.  The  consistency  of  the  mortar  should  not 
change  sensibly  if  the  mixing  be  continued  three 
minutes  after  the  expiration  of  the  required  five 
minutes. 

"2.  If  a  small  quantity  of  the  mortar  be  taken  up 
on  the  trowel  and  allowed  to  fall  upon  the  mixing  slab 
from  a  height  of  50  centimeters  it  should  be  detached 
from  the  trowel  without  leaving  any  small  particles 
adhering,  and  after  falling  should  approximately  retain 
its  form  without  cracking. 


122  HYDRAULIC   CEMENT. 

"  3.  A  small  quantity  taken  in  the  hand  and  patted 
into  a  round  form,  until  water  flushes  to  the  surface, 
should  not  stick  to  the  hand,  and,  when  allowed  to 
fall  from  a  height  of  one-half  meter,  the  ball  should 
retain  its  rounded  form  without  showing  any  cracks." 

To  meet  these  requirements  leaves  but  a  narrow 
limit  within  which  the  consistency  may  vary.  If  a 
slightly  too  small  quantity  of  water  be  used,  the  mor- 
tar would  crack  upon  falling.  If  the  quantity  be  very 
slightly  too  great,  the  mortar  continues  to  soften  upon 
further  working,  becomes  sticky,  and  loses  its  form 
upon  falling. 

Mortar  of  the  dry  consistency  is  used  when  the 
briquette  is  to  be  made  by  beating  the  mortar  into  the 
moulds.  For  this  purpose  the  mortar  is  required  to 
have  the  consistency  of  damp  earth.  In  the  event  of 
moulding  the  briquettes  by  machinery  the  quantity 
of  water  may  perhaps  be  controlled  by  the  amount  of 
compacting  employed  and  the  tendency  to  force  the 
water  out  in  moulding. 

The  quantity  of  water  required,  as  already  noted, 
varies  with  the  fineness,  age,  and  other  conditions  of 
the  cement,  as  well  as  with  its  nature. 

To  bring  mortar  to  a  plastic  condition  the  quantity 
of  water  required  is  approximately  as  follows: 

"  For  briquettes  of  neat  cement:  Portland  cement 
about  25$,  natural  cement  about  30$. 

'  For  briquettes  of   I   part   cement,    I    part  sand: 
about  15$  of  total  weight  of  sand  and  cement. 

"  For  briquettes  of  I  part  cement,  3  parts  sand: 
about  \2%  of  total  weight  of  sand  and  cement," 


TESTS   OF  THE   STRENGTH   OF   MORTAR.          123 

In  any  particular  instance  the  proper  amount  can 
only  be  determined  by  trial. 


ART.  45.     METHODS  OF  MAKING  BRIQUETTES. 

The  wide  differences  commonly  found  in  the  results 
of  tensile  tests  made  by  different  men  are,  without 
doubt,  mainly  due  to  differences  in  making  the 
briquettes.  Probably  if  the  other  strength  tests  were 
as  commonly  used  as  that  of  tension  the  same  want 
of  uniformity  would  be  observable  in  them.  These 
differences  occur,  not  only  in  the  work  of  novices,  but 
in  that  of  skilled  operators,  who,  while  able  to  main- 
tain practical  uniformity  in  their  own  work,  disagree 
in  results  with  each  other  when  experimenting  upon 
the  same  material  and  apparently  using  the  same 
methods.  The  extent  of  this  difficulty  has  already 
been  alluded  to  in  Art.  42. 

In  order  to  secure  uniform  results  it  is  essential 
that  a  uniform  procedure  be  adopted  as  to  all  the 
operations  of  forming  the  briquette.  The  points  of 
importance  are  the  quantity  of  water  used  in  temper- 
ing— which  has  been  discussed  in  the  last  article,  the 
method  of  gauging  and  amount  of  working  to  which 
the  mortar  is  subjected  in  bringing  it  to  a  proper  con- 
sistency, and  the  method  of  forming  the  briquette  and 
amount  of  fopce  used  in  placing  the  mortar  in  the 
mould. 

In  making  briquettes  by  hand  two  general  methods 
are  employed,  corresponding  to  different  consistencies 
of  the  mortar.  The  plastic  method  is  most  commonly 
employed,  being  used  in  England,  France,  and  the 


124  HYDRAULIC   CEMENT. 

United  States,  while  the  dry  method  is  standard  in 
Germany. 

The  rules  recommended  by  the  committee  of  the 
American  Society  of  Civil  Engineers  give  the  follow- 
ing method  of  making  the  briquettes: 

4 '  The  proportions  of  cement,  sand,  and  water  should 
be  carefully  determined  by  weight,  the  sand  and 
cement  mixed  dry,  and  the  water  added  all  at  once. 
The  mixing  must  be  rapid  and  thorough,  and  the 
mortar,  which  should  be  stiff  and  plastic,  should  be 
firmly  pressed  into  the  moulds  with  a  trowel,  without 
ramming,  and  struck  off  level;  the  mould  in  each  in- 
stance while  being  charged  and  manipulated  to  be  laid 
directly  on  glass,  slate,  or  some  other  non-absorbing 
material. 

44  The  moulding  must  be  completed  before  incipient 
setting  begins.  As  soon  as  the  briquettes  are  hard 
enough  to  bear  it,  they  should  be  taken  from  the 
moulds  and  be  kept  covered  with  a  damp  cloth  until 
they  are  immersed.  For  the  sake  of  uniformity,  the 
briquettes,  both  of  neat  cement  and  those  containing 
sand,  should  be  immersed  in  water  at  the  end  of  24 
hours,  except  in  the  case  of  one-day  tests." 

The  report  of  the  French  commission  upon  standard 
tests  recommends  the  following  method: 

"  The  moulds  are  placed  upon  a  plate  of  marble  or 
polished  metal,  which  has  been  well  cleaned  and 
rubbed  with  an  oiled  cloth.  Six  moulds  are  filled 
from  each  gauging  if  the  cement  be  slow-setting  and 
four  if  it  be  quick-setting.  Sufficient  material  is  at 
once  placed  in  each  mould  to  more  than  fill  it.  The 
mortar  is  pressed  into  the  mould  with  the  fingers  so 


TESTS  OF  THE   STRENGTH   OF   MORTAR.          12$ 

as  to  leave  no  voids  and  the  side  of  the  mould  tapped 
several  times  with  the  trowel  to  assist  in  disengaging 
the  bubbles  of  air.  The  excess  of  mortar  is  then 
removed  by  sliding  a  knife  blade  over  the  top  of  the 
mould  so  as  to  produce  no  compression  upon  the 
mortar. 

"  The  briquettes  are  removed  from  the  moulds  when 
sufficiently  firm,  and  are  allowed  to  remain  for  24 
hours  upon  the  plate  in  a  moist  atmosphere,  protected 
from  currents  of  air  or  the  direct  rays  of  the  sun,  and 
at  a  nearly  constant  temperature  of  15°  to  18°  C. 
They  are  then  placed  in  the  surroundings  in  which 
they  are  to  be  kept  until  the  time  for  breaking.  With 
quick-setting  cements  the  delay  is  reduced  from  24 
hours  to  i  hour  for  neat  cement  and  3  hours  for  sand- 
mortar. 

"It  is  recommended  to  weigh  the  briquettes  after 
removing  them  from  the  moulds  to  make  sure  of  the 
regularity  of  their  formation." 

By  the  German  method  the  mortar  is  mixed  with 
less  water  than  in  the  above,  and  the  mould  is  filled 
and  heaped  with  it.  It  is  then  rammed  into  place  and 
pounded  until  the  water  flushes  to  the  surface,  after 
which  the  briquette  is  struck  off  level,  and  when  hard 
enough  is  taken  from  the  mould  and  treated  as  in  the 
other  case.  Following  are  the  specifications  adopted 
by  the  Association  of  German  Cement  Makers:* 

"  On  a  metal  or  thick  glass  plate  five  sheets  of  blot- 
ting-paper soaked  in  water  are  laid,  and  on  these  are 
placed  five  moulds  wetted  with  water.  250  grammes 

*  Engineering  News,  Nov.  13,  1886. 


126  HYDRAULIC   CEMENT. 

of  cement  and  750  grammes  of  standard  sand  are 
weighed  and  thoroughly  mixed  dry  in  a  vessel;  then 
100  cubic  centimeters  of  fresh  water  are  added,  and 
the  whole  mass  mixed  for  five  minutes.  With  the 
mortar  so  obtained  the  moulds  are  at  once  filled,  with 
one  filling,  so  high  as  to  be  rounded  on  top,  the 
mortar  being  well  pressed  in.  By  means  of  an  iron 
trowel,  5  to  8  centimeters  wide,  35  centimeters  long, 
and  weighing  about  250  grammes,  the  projecting 
mortar  is  pounded,  first  gently  and  from  the  sides,  then 
harder  into  the  moulds,  until  the  mortar  grows  elastic 
and  water  flushes  to  the  surface.  A  pounding  of  at 
least  one  minute  is  necessary.  An  additional  filling 
and  pounding  in  of  the  mortar  is  not  admissible,  since 
the  test-pieces  of  the  same  cement  should  have  the 
same  density  at  the  different  testing  stations.  The 
mass  is  now  cut  off  with  a  knife  and  the  surface 
smoothed.  The  mould  is  carefully  taken  off,  and 
the  test-piece  placed  in  a  box  lined  with  zinc,  which 
is  to  be  provided  with  a  cover  to  prevent  a  non-uni- 
form drying  of  the  test-pieces  at  different  tempera- 
tures." 

For  making  the  test-pieces  of  neat  cement :  ' '  The 
inside  of  the  moulds  are  slightly  oiled,  and  the  same 
are  placed  on  a  metal  or  glass  plate  without  blotting- 
paper.  1000  grammes  of  cement  are  weighed  out, 
200  grammes  of  water  added,  and  the  whole  mass 
thoroughly  mixed  for  five  minutes.  The  forms  are 
well  filled,  and  then  proceed  as  for  hand-work  with 
sand-mortar. 

"  The  mould  can  only  be  taken  off  after  the  cement 
has  sufficiently  hardened. 


TESTS  OF  THE   STRENGTH   OF  MORTAR.          1 27 

"  The  quantity  of  water  for  finely-ground  or  quick- 
setting  cements  must  be  increased." 

A  method  somewhat  in  use  in  France  for  sand- 
mortar  is  that  proposed  by  M.  Candlot,  and  recom- 
mended by  the  Commission  upon  Methods  of  Testing 
Materials,  for  use  with  sand-mortars.  It  is  as  follows: 

"  Sufficient  mortar  is  gauged  at  once  to  make  six 
briquettes,  requiring  250  grammes  of  cement  and  750 
grammes  of  normal  sand.  The  weight  of  water  neces- 
sary exceeds  by  30  grammes  the  amount  necessary  to 
bring  the  cement  alone  to  normal  consistency. 

The  mortar  is  prepared  in  the  ordinary  manner.  In 
forming  the  briquette  the  mould  is  placed  upon  a 
metal  plate,  and  a  guide  fitted  above  it  having  the 
same  section  as  the  mould  and  a  height  of  125  millim- 
eters. 

"  1 80  grammes  of  mortar  are  introduced  and  roughly 
distributed  in  the  mould  and  guide  with  a  rod.  By 
means  of  a  metallic  pestle  weighing  one  kilogramme, 
and  with  a  base  of  the  form  of  the  briquette  but  of 
slightly  less  dimensions,  the  mortar  is  pounded  softly 
at  first,  then  stronger  and  stronger  until  a  little  water 
escapes  under  the  bottom  of  the  mould. 

"  The  pestle  and  guide  are  then  removed  and  the 
mortar  cut  off  level  with  the  top  of  the  mould." 

It  is  claimed  that  by  this  method  very  uniform 
results  have  been  obtained. 

There  are  two  points  to  be  especially  noted  in  mak- 
ing briquettes  by  hand:  first,  the  mortar  must  be  very 
thoroughly  worked  in  gauging;  both  the  German  and 
French  rules  require  that  it  shall  be  briskly  mixed  for 
at  least  five  minutes,  only  sufficient  mortar  being  pre- 


128  HVDRAULIC  CEMENT. 

pared  at  once  for  five  or  six  briquettes;  second,  the 
air- bubbles  must  be  well  worked  out  of  the  mortar  in 
filling  the  moulds.  The  neglect  of  these  precautions 
causes  much  of  the  irregularity  which  commonly  exists 
in  the  work  of  inexperienced  operators. 

It  is  perhaps  easier  to  secure  uniform  results  with 
the  dry  than  with  the  plastic  method.  The  greater 
density  of  the  hammered  briquette  also  gives  it  higher 
strength.  The  plastic  method,  however,  accords  more 
nearly  with  the  conditions  of  the  use  of  the  material 
in  practice. 

Even  with  the, most  experienced  operators  there 
exist  differences  in  the  amount  of  working,  the  pres- 
sure given  in  forming  the  briquette,  and  the  quantity 
of  water  used,  which  cause  wide  variations  in  result. 

In  order  to  secure  good  results  in  tests  of  strength 
it  is  necessary  that  the  briquettes  should  be  kept  in  a 
moist  condition  during  setting  and  the  first  period  of 
hardening.  For  this  purpose  it  is  customary  in  the 
United  States  to  cover  the  briquettes  with  wet  cloths 
after  moulding  and  until  submerging  them.  In 
Europe  they  are  commonly  placed  in  zinc  boxes  dur- 
ing this  period. 

In  the  laboratory  of  the  City  of  Philadelphia  Mr. 
Richard  L.  Humphreys  uses  a  soapstone  closet  for 
this  purpose.  He  describes  *  the  arrangement  as 
follows:  "  This  closet,  which  is  made  of  soapstone  i£ 
inches  thick,  is  supported  on  a  wooden  frame,  and  is 
3  feet  high  and  18  inches  wide.  Along  the  front  is  a 
strip  of  soapstone  3  inches  wide,  forming  a  basin  of 

Proceedings  Engineers'  Club  of  Philadelphia,  November,  1896. 


TESTS  OF  THE  STRENGTH  OF  MORTAR.         1 29 

the  bottom  of  the  closet,  in  which  water  is  placed  for 
keeping  the  air  moist.  The  doors  are  made  of  wood, 
covered  with  planished  sheet  copper,  and  are  rabbeted 
to  fit  tightly.  There  are  two  sets  of  shelves,  the 
lower  being  a  wooden  rack,  and  the  upper  is  formed 
of  strips  of  glass  33  inches  long,  3  inches  wide. 
When  closed  the  closet  is  perfectly  tight,  the  water 
in  the  bottom  keeping  the  air  moist,  preventing  the 
briquettes  from  drying  out,  and  thus  checking  the 
process  of  setting. 

"  Briquettes  which  have  been  removed  from  the 
moulds  are  placed  on  edge  on  the  glass  shelves,  while 
the  moulds  containing  the  briquettes  too  soft  to  be 
removed  are  placed  on  the  rack." 

ART.  46.     MECHANICAL  APPLIANCES  FOR  MAKING 
BRIQUETTES. 

In  order  to  reduce  the  effect  of  the  personality  of 
the  operator  in  making  tests  of  the  strength  of  cem- 
ents, various  appliances  for  gauging  and  moulding 
briquettes  by  machinery  have  been  proposed  and  tried. 

Greater  uniformity  in  these  tests  is  highly  desirable, 
and  it  seems  possible  to  reach  it  only  by  the  applica- 
tion of  automatic  appliances  in  making  the  briquettes. 

No  entirely  satisfactory  system  of  automatic  testing 
has  as  yet  been  devised.  In  Europe  machines  are 
quite  commonly  employed  for  moulding  briquettes, 
but  the  mixing  is  done  by  hand  in  the  ordinary 
manner. 

In  Germany  and  Switzerland  all  blocks  for  compres- 
sive  tests  are  made  by  machine,  as  are  many  of  the 


130 


HYDRAULIC   CEMENT. 


tensile  specimens.  The  machine  used  for  this  purpose 
is  either  the  Bohme  hammer  or  the  Tetmajer  appa- 
ratus. 

The  Bohmt  hammer,  designed  by  Dr.  Bohm6  of  the 
Charlottenburg  Experiment  Station,  is  shown  in  Fig. 
II.  It  consists  of  an  arrangement  by  which  the  mor- 


FlG.   II. 

tar  is  compacted  in  the  mould  by  a  succession  of 
blows  struck  by  a  hammer  of  the  weight  of  two 
kilogrammes  upon  a  plunger  sliding  in  a  guide-mold 
placed  over  the  mold  in  which  the  briquette  is  to  be 
formed. 

The  machine  is  arranged  to  lock  after  striking  150 
blows.  A  high  degree  of  density  is  thus  produced  in 
the  briquette,  and  the  air  is  thoroughly  expelled. 
More  regular  results  are  thus  obtained,  depending 
much  less  upon  the  personality  of  the  operator  than 
by  the  hand  method.  The  arrangement  of  this 
apparatus,  however,  is  such  that  its  operation  must  be 
extremely  slow,  in  order  to  give  time  for  the  hammer 


TESTS   OF   THE   STRENGTH    OF  MORTAR.          13! 

to  strike  a  full  blow  without  being  caught  on  the  next 
stroke,  and  the  time  required  to  make  a  briquette  is 
too  great  to  admit  of  its  general  use. 

The  rules  of  the  Association  of  German  Cement 
Makers  specify  this  machine,  and  are  as  follows:*  "  In 
order  to  obtain  concordant  values  in  compression  tests 
machine-making  is  necessary.  400  grammes  of  neat 
cement  and  1200  grammes  of  dry  standard  sand  are 
thoroughly  mixed  dry  in  a  vessel,  160  cubic  centi- 
meters of  water  are  added  thereto,  and  then  the 
mortar  is  thoroughly  mixed  for  five  minutes.  Of  this 
mortar  860  grammes  are  placed  in  the  cubic  mould, 
provided  with  guide-mould,  and.  the  mould  is  then 
screwed  on  the  bed-plate  under  the  pounding-machine. 
The  iron  follower  is  placed  in  the  form,  and  by 
means  of  Bohme's  trip-hammer  one  hundred  and  fifty 
blows  are  struck  by  a  hammer  weighing  2  kilogrammes. 
After  removing  the  guide-mould  and  follower  the  test- 
piece  is  smoothed  off,  taken  with  the  mould  from  the 
bed-plate,  and  then  treated  as  for  hand-work." 

The  Tetmajer  apparatus  is  similar  in  character  to 
the  Bohme  hammer.  It  consists  of  an  iron  rod  carry- 
ing a  weight  upon  its  lower  end,  which  is  raised 
through  a  given  height  and  dropped  upon  the  mortar 
in  the  mould.  The  ram  in  this  machine  weighs  3 
kilograms.  This  machine  is  used  in  the  Zurich 
laboratory  for  both  tensile  and  compressive  specimens, 
and  Prof.  Tetmajer  regulates  the  number  of  blows  by 
requiring  a  certain  amount  of  work  to  be  done  upon 
a  unit  volume  of  mortar, — 0.3  kilogrammeter  of 

*  Engineering  News i  Nov.  13,  1886. 


132  HYDRAULIC   CEMENT. 

work  per  gramme  of  dry  material  of  which  the  mortar 
is  composed.  This  apparatus  is  subject  to  the  same 
limitations  in  practice  as  the  Bohme  hammer,  in  being 
very  slow  in  use,  and  somewhat  expensive  in  first  cost 
of  apparatus. 

Canadian  Method. — In  Canada,  and  to  some  extent 
in  England,  the  method  has  been  adopted  of  gauging 
the  mortar  quite  soft,  using  a  high  percentage  of 
water,  with  machine-mixing,  and  then  moulding  the 
briquettes  under  light  pressure — 20  Ibs.  per  square 
inch  on  the  surface  of  the  briquette.  This  gives  much 
lower  results  for  strength  than  the  ordinary  methods, 
which  is  unimportant  provided  the  results  are  con- 
cordant, and  specifications  are  made  to  agree  with  the 
method. 

A  number  of  tests  made  by  Mr.  Cecil  B.  Smith  at 
the  McGill  University  seem  to  show  that  the  method 
is  capable  of  yielding  uniform  results  in  so  far  as  the 
variations  of  the  individual  tests  from  the  mean  of  a 
single  series  is  concerned.  The  method  appears  to 
be  defective,  however,  in  not  affording  a  satisfactory 
method  of  determining  the  proper  consistency  of  the 
mortar,  upon  which  largely  depends  the  comparability 
of  the  results  of  different  observers. 

The  Jamieson  briquette  machine,  shown  in  Fig.  12, 
was  designed  by  Prof.  Jamieson,  of  the  Iowa  State 
University,  for  the  purpose  of  making  briquettes  under 
diect  pressure,  and  is  intended  to  secure  rapid  manip- 
ulation. 

The  following  description  is  from  Engineering  News 
of  February  7,  1891  :  "  The  principle  of  the  machine 
is  very  simple.  A  vertical  cylinder  (#)  whose  cross- 


TESTS   OF  THE   STRENGTH   OF   MORTAR. 


133 


section  conforms  to  the  outline  of  the  standard  bri- 
quette receives  a  charge  of  the  mixed  cement  from  a 


FIG.  12. 


hopper  at  the  side.     In  this  cylinder  a  close-fitting 
piston    is   worked    by  a  hand-lever  (&),   so   that   the 


134  HYDRAULIC   CEMENT. 

charge  of  cement  in  the  cylinder  may  be  subjected  to 
a  pressure  of  about  175  Ibs.  per  square  inch.  The 
bottom  of  the  cylinder  is  raised  above  the  bed-plate  a 
distance  equal  to  the  thickness  of  the  briquette  (i  inch), 
and  in  this  space  works  a  triangular  block  (/)  having 
two  holes  of  the  same  cross-section  as  the  briquette. 
This  block  can  be  oscillated  to  bring  either  of  these 
holes  beneath  the  cylinder.  When  one  hole  is  in  this 
position,  however,  the  other  is  clear  of  the  cylinder  at 
one  side,  and  the  briquette  of  cement  which  has  been 
pressed  into  it  can  be  lifted  by  a  plunger,  worked  by 
•a  lever  (;;/)  and  guided  by  the  pins  (kk).  Owing  to 
the  pressure  used  the  briquettes  are  hard  enough  to 
handle  as  soon  as  lifted  from  the  mould,  and  they  are 
at  once  removed  and  placed  on  a  glass  slab." 

"  In  practical  working  it  has  been  found  possible 
to  make  briquettes  as  rapidly  as  600  per  hour." 

This  machine  may  be  found  useful  in  laboratories 
where  large  numbers  of  briquettes  are  needed  for  the 
purpose  of  comparing  cements  under  various  condi- 
tions, as  it  greatly  lessens  the  manual  labor  of  form- 
ing the  briquette.  It  is  to  be  observed,  however, 
that  the  time  occupied  in  making  briquettes  is  largely 
used  in  mixing  the  mortar,  and  that  rapid  moulding 
involves  equally  rapid  mixing.  Ihe  macnine,  as 
designed,  provides  no  means  of  regulating  the  amount 
of  pressure  applied  in  forming  the  briquette,  which 
may  vary  with  different  operators,  and  is  thus  likely 
to  produce  variations  in  result.  This  may  be  com- 
paratively unimportant  for  neat  briquettes  mixed  dry, 
but  has  a  large  influence  upon  the  strength  of  sand- 
mortar.  It  may  be  suggested  also  that  to  make 


TESTS   OF  THE   STRENGTH   OF   MORTAR.          13$ 

by  this  method  briquettes,  which  are  firm  enough  to 
handle  immediately,  the  cement  must  be  mixed  very 
dry — too  dry  for  the  best  results;  with  sand-mortars 
it  will  be  very  difficult  to  produce  solid  cakes  by  this 
method. 

The  experience  of  the  author  in  experimenting  with 
various  appliances  for  moulding  briquettes  shows 
that  quite  uniform  results  may  be  obtained  from 
briquettes  moulded  under  a  single  application  of  a 
steady  pressure. 

This  method  may  be  applied  much  more  rapidly 
than  the  hammer  method,  with  about  as  good  results, 
and  render  the  results  of  different  operators  much 
more  concordant  than  can  be  obtained  by  hand-work, 
although  the  variations  from  the  mean  in  the  work  of 
a  single  observer  may  be  as  great  or  greater  than  in 
the  hand-work. 

Briquettes  of  neat  cement,  machine-mixed,  and 
moulded  under  a  pressure  of  about  500  Ibs.,  upon  the 
surface  of  the  briquette,  give  good  results  when  the 
averages  of  different  men  are  compared,  and  small 
variations  in  pressure  are  not  important  in  the  results. 

For  sand-mortar,  one  part  cement  to  three  parts 
sand,  a  pressure  of  IOOO  to  1500  Ibs.  is  desirable  to 
sufficiently  compact  the  mortar  to  form  homogeneous 
briquettes  and  give  uniformity  in  the  results. 

To  obtain  the  best  results  the  mortar  should  be 
gauged  to  such  a  consistency  that  the  water  begins  to 
ooze  out  under  the  pressure,  the  cakes  being  reduced 
to  a  semi-plastic  condition,  and  becoming  too  soft  to 
handle  before  setting. 

An  apparatus  for  making  briquettes  by  this  method 


136  HYDRAULIC    CEMENT. 

is  easily  arranged.  To  do  good  work  it  should  not 
aim  at  too  great  rapidity,  but  sufficient  time  should 
be  given  to  each  briquette  to  permit  the  weight  to 
produce  its  full  effect  in  the  compression  of  the  mortar. 
The  gradual  application  of  the  load  in  a  testing-ma- 
chine has  been  found  preferable  to  the  sudden  descent 
of  a  lever  as  usually  employed.  Possibly  a  screw  and 
hand-wheel  giving  a  gradually  increasing  pressure  may 
prove  the  best  method  of  applying  the  pressure.  The 
time  occupied  need  not  be  long,  and  briquettes  may 
be  made  much  more  rapidly  than  in  hand-work.  A 
means  of  regulating  the  pressure  so  that  it  may  always 
be  the  same  is  an  essential  to  good  work. 

It  is  quite  as  important  to  eliminate  the  personal 
element  from  the  gauging  as  from  the  moulding  of 
briquettes.  For  this  purpose  several  appliances  have 
been  tried. 

Thejigmixcr  is  an  apparatus  in  which  the  materials 
are  placed  in  cups  with  covers  clamped  on,  and  shaken 
rapidly  up  and  down.  It  has  been  tried  in  a  number 
of  places,  but  has  usually  been  found  quite  unsatisfac- 
tory in  practice.  It  is  difficult  to  make  a  satisfactory 
mixture  by  this  method,  and  the  result  depends  very 
much  upon  the  rapidity  of  operation. 

The  Faija  mixer  was  designed  and  first  used  by  Mr. 
Faija  in  England.  It  is  shown  in  Fig.  13,  as  made 
by  Riehle  Bros.  Testing  Machine  Company  of  Phila- 
delphia, and  consists  of  a  cylindrical  pan  in  which  a 
mixer,  formed  of  four  curved  blades,  revolves  both  on 
its  own  axis  and  about  that  of  the  pan.  This  arrange- 
ment gives  fairly  good  results  in  use. 

Fig.  14  shows  an  arrangement  used  by  the  author 


TESTS   OF   THE    STRENGTH    OF   MORTAR. 


137 


in  the  laboratory  of  the  College  of  Civil  Engineering 
at  Cornell  University. 

In  this  apparatus  the  cylinder  containing  the  ma- 
terials is  closed,  thus  avoiding  the  dust,  which  is  very 
disagreeable  with  the  open  pan.  The  cover  revolves 
about  the  axis  of  the  cylinder,  and  the  gear  is  placed 


FIG.  13. 


FIG.  14. 


outside  to  remove  any  danger  of  it  becoming  clogged. 
The  mixer  is  formed  of  vertical  rods  held  by  a  hori- 
zontal arm,  and  revolves  about  the  axis  of  the  cylinder 
and  also  about  the  middle  point  of  the  arm.  This 
arrangement  seems  to  give  a  somewhat  more  thorough 
working  of  the  mortar  than  the  same  number  of  turns 
of  the  Faija  mixer,  but  if  the  briquettes  be  moulded 
under  heavy  pressure  the  two  give  about  the  same 
results. 

By  the  use  of  some  apparatus  of  this  kind  the  mor- 
tar may  be  much  more  expeditiously  mixed  than  by 
hand,  and  with  greater  uniformity. 


138  HYDRAULIC   CEMENT. 

To  devise  any  system  of  making  briquettes  by  hand 
which  will  secure  uniformity  in  the  work  of  different 
men  seems  hopeless.  If  such  uniformity  is  to  be 
secured,  it  must  be  by  the  use  of  automatic  appliances. 
This  involves  not  only  the  use  of  the  same  apparatus, 
but  its  use  in  the  same  manner  in  the  different  labora- 
tories. This  would  be  very  difficult  of  attainment; 
but  if  various  mechanical  appliances  should  come  into 
use  the  relations  between  them  would  soon  become 
known,  and  statements  of  the  means  employed  in  form- 
ing briquettes  would  make  the  results  to  a  certain 
extent,  at  least,  comparable  with  each  other. 

For  the  purpo'se  of  securing  uniformity  in  the 
results  of  pressure-made  briquettes  the  following  pro- 
cedure has  been  followed,  with  good  results,  in  the 
laboratory  of  the  College  of  Civil  Engineering  at  Cor- 
nell University:  In  gauging  the  mortar  two  pounds 
of  the  dry  materials  are  employed  in  one  mixing.  For 
sand-mortar,  the  dry  materials  are  put  in  the  mixer 
and  given  50  turns;  the  water  is  then  added  and  the 
mixing  completed  by  an  additional  50  turns,  the 
mixer  being  operated  at  the  rate  of  about  100  turns 
per  minute.  With  neat  cement,  the  cement  is  put  in 
the  mixer,  the  water  added,  and  the  mixing  completed 
with  50  turns  of  the  handle.  After  the  completion 
of  the  mixing  the  mould  and  guide  are  filled  with  the 
mortar,  and  a  pressure  of  1000  Ibs.  put  upon  the 
piston  in  the  pressure-machine.  The  piston  is  then 
raised,  the  guide  removed,  and  the  surplus  of  mortar 
sliced  off;  after  which  the  briquette  is  removed  from 
the  mould  by  being  pressed  out  upon  the  surface  upon 
which  it  is  to  remain  until  set.  The  necessary  quan- 


TESTS   OF  THE   STRENGTH   OF   MORTAR.          139 

tity  of  water  is  first  determined  by  trial,  and  is  such 
that  the  pressure  used  will  cause  the  water  to  slightly 
ooze  out  beneath  the  mould. 

ART.  47.     TENSILE  TESTS. 

The  test  for  tensile  strength  is  commonly  made  by 
placing  the  briquette  in  a  pair  of  clips  which  catch  its 
ends  and  are  attached  to  a  machine  by  which  the  load 
necessary  to  break  the  briquette  may  be  weighed.  In 
order  to  secure  uniform  results  it  is  necessary  that  the 
stress  shall  be  so  applied  as  to  bring  the  tension 
axially  upon  the  small  section  of  the  briquette,  and 
also  that  the  rate  of  application  of  the  load  shall  be 
always  the  same. 

There  are  various  types  of  testing-machines  in  use, 
and  it  seems  unnecessary  to  enter  into  any  detailed 
description  of  them  here.  One  of  the  simplest  is  the 
old  machine  in  the  College  of  Civil  Engineering  at 
Cornell  University,  which  consists  of  a  lever,  suspended 
from  a  wooden  framework,  carrying  near  one  end  the 
clips  to  hold  the  specimen,  and  at  the  other  a  bucket 
into  which  a  stream  of  water  flows  until  the  briquette 
breaks,  when  the  water  is  shut  off  automatically. 
The  weight  of  water  multiplied  by  the  ratio  of  lever- 
arms  gives  the  stress  on  the  briquette.  All  of  the 
points  of  suspension  are  on  knife-edges,  and  an  adjust- 
able weight  upon  one  end  serves  to  balance  the  lever. 

The  Michaelis  Machine,  shown  in  Fig.  15,  is  similar 
in  character  to  the  above,  but  is  arranged  with  a 
double  lever,  and  uses  shot  in  the  bucket  instead  of 
water.  This  machine  is  the  one  commonly  employed 
in  Europe. 


FIG.  16. 


TESTS   OF  THE   STRENGTH   OF   MORTAR  14! 

The  Fairbanks  Machine  is  practically  tne  same  as 
that  of  Michaelis.  In  the  Fairbanks  machine  the  shot 
is  weighed  and  the  stress  determined  by  the  same 
beam  used  in  breaking  the  specimen,  the  bucket  being 
hung  at  the  other  end  of  the  beam  from  that  used  in 
breaking  the  specimen,  and  the  weight  found  by 
means  of  a  sliding  weight. 

The  Richie  Mac/tine,  shown  in  Fig.  16,  is  an  ordi- 
nary lever  machine  in  which  the  load  is  brought  upon 
the  specimen  by  means  of  the  lower  hand-wheel,  while 
the  weight  is  moved  along  the  scale-beam  by  the 
upper  hand-wheel.  In  testing  a  briquette  both  wheels 
must  be  operated  simultaneously  and  the  scale-beam 
be  kept  balanced. 

The  Olsen  Machine,  shown  in  Fig.  17,  is  similar  in 
character  to  the  above,  but  differs  somewhat  in  detail. 
This  machine  has  been  modified  by  Prof.  Porter  in 
one  constructed  for  Lafayette  College,*  by  adding  a 
second  lever  below  the  clips,  through  which  the  stress 
is  applied  by  means  of  water  flowing  into  a  bucket 
attached  to  its  end.  The  stress  is  measured  by  the 
weight  sliding  upon  the  upper  scale-beam  as  in  the 
ordinary  machine,  but  the  weight  is  moved  auto- 
matically by  means  of  an  electric  contact  at  the  end 
of  the  beam. 

Various  other  more  complicated  types  of  machines 
are  sometimes  employed,  most  of  them  hydraulic  in 
principle. 

Nearly  any  of  the  machines  in  common  use  may 
give  good  results  in  practice.  In  selecting  a  machine, 

*  Engineering  News,  March  5,  1896. 


142 


HYDRAULIC   CEMENT. 


however,  those  are  to  be  preferred  in  which  the  load 
may  be  automatically  applied  at  a  uniform  rate.     The 


FIG.  17. 

attainment   of  a  constant  rate  of  application  with  a 
hand-machine  is  a  matter  of  considerable  difficulty. 

In  order  that  the  stress  upon  the  briquette  shall  be 
axial,  care  must  be  exercised  in  properly  centring  the 


TESTS   OF  THE   STRENGTH    OF  MORTAR.          143 

briquette  in  the  clips,  and  the  form  of  the  clip  must 
be  such  that  it  shall  not  clamp  or  bind  upon  the  head 
of  the  briquette,  but  may  be  free  to  adjust  itself  to  an 
even  bearing.  The  surface  of  contact  between  the  clip 
and  briquette  must  be  large  enough  to  prevent  the 
material  of  the  briquette  being  crushed  at  the  point  of 
contact,  and  yet  as  small  as  possible  to  admit  of  its 
more  free  self-adjustment.  The  suspension  of  the 
clips,  as  is  usual,  by  conical  bearings  permits  them  to 
turn  so  as  to  always  transmit  the  stress  in  a  right  line 
between  bearings. 

Fig.  1 8  shows  the  form  of  clip  which  is  used  with 


FIG.  18. 

the  standard  German  briquette.  As  here  given  it  is 
approved  by  the  "  Commission  des  M£thodes  d'Essai 
des  Materiaux  de  Construction,"  as  giving  very  satis- 
factory results. 

With  the  briquette  used   in  the  United  States  and 


144 


HYDRAULIC   CEMENT. 


England  several  forms  have  been  used  for  clips.  Fig. 
19  shows  the  form  adopted  by  the  Committee  of  the 
American  Society  of  Civil  Engineers.  This  form  does 
not  offer  sufficient  bearing-surface  for  good  results,  as 
the  briquette  is  likely  to  break  on  account  of  the 
crushing  of  the  surface  of  the  briquette  at  the  point 
of  contact. 

The  form  shown  in  Fig.  20  has  been  much  used,  but 


FIG.  19.  FIG.  20. 

has  the  disadvantage  of  clamping  the  head  of  the 
briquette  too  closely,  and  unless  great  care  is  used 
may  cause  the  briquette  to  break  by  twisting,  thus 
giving  irregular  results.  When  the  break  occurs 
through  the  crushing  of  the  material  the  fracture 
usually  extends  from  one  of  the  points  of  contact 
irregularly  to  the  small  section,  but  a  break  due  to 
twisting  may  often  be  a  centre  break,  and  the  irregu- 
larity show  only  in  the  results. 

The  form  of  clip  shown  in  Fig.  21  is  to  be  preferred 
to  those  given  above,  as  affording  a  sufficient  bearing- 


TESTS   OF  THE   STRENGTH   OF    MORTAR.          145 

surface  without  clamping,  and  thus  tending  to  diminish 
the  irregularities  in  the  results  of  tests. 

In  order  to  prevent  crushing  at  the  points  of  contact 


FIG.  21. 

and  to  permit  more  free  adjustment  Mr.  W.  R.  Cock 
has  proposed*  a  rubber  bearing,  as  shown  in  Fig  22. 
The  use  of  this  clip  undoubtedly  increases  to  some 
extent  the  proportion  of  centre  breaks,  and  perhaps 
slightly  raises  the  breaking  strength.  A  rubber  bear- 
ing-surface may  also  be  secured  on  the  clips  of  form 
shown  in  Fig.  21,  by  stretching  a  rubber  band  around 
the  jaw  of  the  clip  so  as  to  cover  the  surface  of  con- 
tact. This  may  somewhat  increase  the  regularity  of 
the  tests,  but  when  carefully  used  the  ordinary  clip  is 
capable  of  giving  very  satisfactory  results. 

Various  appliances  have  been  proposed  for  the  accu- 
rate centring  of  briquettes,  or  to  prevent  the  more  free 
adjustment  of  the  clips  to  the  direction  of  stress,  by 

*  Engineering  News,  Dec.  20,  1890. 


146  HYDRAULIC   CEMENT. 

using  a  template  for  the  exact  placing  of  the  briquette, 
or  by  hinging  the  clips  at  the  upper  corners.  These 
arrangements  do  not,  however,  seem  to  be  necessary. 


FIG.  22. 

The  method  of  keeping  the  briquettes  between  the 
time  of  moulding  and  breaking  is  of  course  important 
in  its  effect  upon  the  resulting  strength.  The  tem- 
perature should,  for  standard  tests,  always  be  kept  as 
nearly  uniform  as  possible — between  60°  and  70°  Fahr. 
When  the  mortar  has  been  conserved  under  water  it 
should  be  tested  immediately  on  being  taken  from  the 
water. 

The  standard  rate  of  applying  the  load  is  ordinarily 
about  400  Ibs.  per  minute. 

ART.  48.    COMPRESSIVE  TESTS. 

The  compressive  strength  of  cement-mortar  is  much 
greater  than  its  tensile  strength,  and  as  it  does  not 


TESTS   OF   THE   STRENGTH   OF   MORTAR.          147 

seem  to  give  a  better  indication  of  value,  while  more 
difficult  of  satisfactory  determination,  and  also  requires 
heavier  apparatus,  it  is  not  usually  employed  as  a  test 
of  quality  in  the  acceptance  of  material.  The  com- 
pressive  test  is,  however,  valuable  for  purposes  of 
comparison,  and  is  desirable  as  an  addition  to  the 
showing  made  by  the  tensile  test.  In  the  European 
experiment  stations  it  is  customary  to  test  all  cements 
under  compression  as  well  as  tension. 

For  this  test,  as  for  tension,  it  is  essential  that  a 
standard  method  be  followed  if  comparable  results  are 
to  be  obtained.  The  size  and  shape  of  the  specimen 
are  of  the  greatest  importance.  The  effect  of  com- 
pression is  ordinarily  to  cause  the  material  to  spread 
laterally  by  pressing  out  the  sides,  failure  usually 
occurring  by  shearing  along  surfaces  inclined  at  about 
30°  with  the  vertical,  leaving  pyramidal  or  conical 
blocks  at  the  middle. 

When  the  specimen  is  small  in  height  the  resistance 
is  greater  per  unit  area  than  if  it  be  higher,  and  for 
blocks  similar  in  form  the  resistance  increases  with  the 
size.  Cubes  are  commonly  employed  for  this  purpose, 
but  cylinders  are  sometimes  preferred,  on  account  of  the 
greater  ease  with  which  homogeneous  specimens  may  be 
prepared,  and  because  of  the  liability  of  the  corners  of 
cubes  to  crack  off  under  comparatively  light  pressure. 

The  common  piece  in  Europe  is  a  cube  with  edges 
7  centimeters  long,  moulded  under  the  hammer,  and 
in  testing  it  is  required  that  the  pressure  be  always 
exerted  on  two  faces  of  the  cube,  that  is,  on  the  faces 
which  are  against  the  surface  of  the  mould,  in  forming 
the  block. 


148  HYDRAULIC   CEMENT. 

The  German  conference  at  Berlin,  however,  recom- 
mended the  use  of  blocks  5  square  centimeters  in  area, 
the  same  as  the  tensile  specimens. 

The  French  "  Commission  on  Methods  of  Testing 
Materials"  made  the  following  recommendations: 

"  For  tests  of  compressive  strength  the  half- 
briquettes  separated  by  tension  are  to  be  used.  Each 
half-briquette  to  be  crushed  separately,  and  the  sum  of 
the  two  results  taken  as  the  strength  of  the  specimen. 

"  In  the  absence  of  half-briquettes  cylinders  45 
millimeters  in  diameter  and  22  millimeters  high  may 
be  used,  made  and  conserved  like  the  tensile  briquettes. 

"  Those  specimens  which  show  visible  irregularities 
or  distortions  are  smoothed  by  lightly  rubbing  in  the 
hand  upon  a  stone  surface." 

"  The  testing  apparatus  should  be  so  arranged 
that  the  stress  may  be  continuously  applied  at  such 
a  rate  as  to  crush  the  half-briquette  in  one  or  two 
minutes." 

"  For  tests  having  for  their  object  the  comparison 
of  mortar  with  other  materials,  it  is  provisionally 
recommended  to  employ  the  cube,  with  faces  of  50 
square  centimeters  area,  placed  upon  one  side.  These 
tests  will  thus  conform  in  a  general  way  to  the  rules 
adopted  for  the  other  materials." 

In  testing  cement  the  compressive  specimens  may 
be  readily  obtained  with  smooth  faces,  which  may  be 
placed  in  the  jaws  of  the  testing-machine  directly  in 
contact  with  tne  compression-blocks.  This  is  the 
usual  practice  in  Europe. 

It  is  common,  however,  in  testing  other  materials, 
stone  or  brick,  to  set  the  specimen  in  the  machine 


TESTS   OF   THE   STRENGTH   OF   MORTAR.          140 

with  a  thin  layer  of  plaster  of  Paris  between  the  plate 
of  the  machine  and  the  surface  of  the  specimen.  A 
small  pressure  being  placed  upon  the  specimen  before 
the  plaster  of  Paris  sets,  the  bearing  becomes  even  and 
the  load  uniformly  distributed  over  the  surface.  In 
many  instances  this  seems  to  conduce  to  greater 
uniformity  in  results  with  cement,  but  it  is  not  com- 
mon practice  and  is  hardly  necessary. 

For  making  compressive  tests  of  cement,  any  of  the 
ordinary  lever  or  hydraulic  machines  in  common  use, 
with  a  capacity  of  40,000  to  50,000  Ibs.,  is  usually 
sufficient.  It  is  desirable  that  the  load  be  applied  as 
uniformly  as  possible,  as  the  result  will  be  more  or 
less  affected  by  unsteadiness  or  shocks. 

A  very  handy  and  efficient  machine  for  this  purpose 
in  use  at  the  College  of  Civil  Engineering,  Cornell 
University,  is  shown  in  Fig.  23.  It  is  a  hydraulic 
machine,  constructed  by  J.  Amsler,  Lafon  &  Son, 
Shiffhausen,  Switzerland.  The  machine  is  a  hydraulic 
press,  in  which  fluid  pressure  is  reduced  through  a 
system  of  pistons,  so  that  it  can  be  measured  by  a 
mercury  manometer.  A  is  the  compression-piston,  B 
and  C  are  the  pistons  which  reduce  the  pressure  exist- 
ing under  piston  A.  The  mercury  manometer  consists 
of  a  glass  tube  connected  at  the  bottom  with  the  space 
under  the  piston  C. 

The  test-piece  E  is  placed  between  the  compression- 
plates,  of  which  one  rests  upon  a  spherical  surface  in 
the  piston  A,  so  that  it  can  adjust  itself;  the  other 
hangs  on  the  end  of  the  hand-screw,  and  may  be  placed 
at  any  height. 

The   cylinder  K  is  filled  with  castor-oil.      The  rod 


1 50  HYDRAULIC   CEMENT. 

L  may  be  driven  into  the  cylinder  by  the  crank  and 
screw,  producing  a  pressure  on  the  oil  between  pistons 
A  and  B.  The  piston  A  presses  upward  on  the  sped- 


FIG.  23. 

men,  while  piston  B  presses  downward  upon  the  larger 
piston    C,    causing    pressure    on    the    fluid    beneath. 
Under  piston  C  is  a  layer  of  machine-oil,  which  serves 
the  purpose  of  making  it  tight  and  lubricating  it. 
The  mercury  fills  the  bottom  of  cylinder  M  (under 


TESTS   OF  THE   STRENGTH   OF   MORTAR.          15 1 

the  machine-oil)  and  the  pipes  connecting  this  cylin- 
der with  the  manometer,  which  stands  at  the  side  of 
the  machine  and  reads  to  32,000  kilogrammes. 

The  pistons  are  fitted  accurately  to  the  cylinders, 
and  are  not  packed.  When  the  machine  is  operated 
by  turning  the  crank  which  drives  the  rod  L  the  pis- 
tons C  and  B  are  caused  to  oscillate  about  their  axes, 
thus  equalizing  the  wear  and  eliminating  the  friction. 
This  machine  is  easily  operated  by  hand,  and  the 
speed  may  be  regulated  by  watching  the  manometer 
while  turning  the  crank. 

It  has  been  proposed  to  employ  punching  tests 
instead  of  crushing  the  entire  specimen.  This  method 
has  been  employed  for  a  number  of  years  in  the  labo- 
ratory at  Teil,  France.  A  punch  five  square  centi- 
meters in  section  (circular)  is  employed,  and  it  is 
claimed  that  the  results  are  more  regular  than  those 
obtained  by  crushing  the  entire  specimen,  while  requir- 
ing less  force  in  the  testing-machine.  The  "  Com- 
mission des  Methodes  d'Essai  des  Materiaux,"  how- 
ever, concluded  that  it  presented  no  advantage  over 
the  ordinary  test. 

ART.  49.     TRANSVERSE  TESTS. 

Tests  of  the  strength  of  mortar  under  transverse 
loading  are  seldom  employed  as  a  measure  of  the 
quality  of  the  material,  but  are  frequently  made  with 
a  view  to  determining  the  action  of  the  material  in 
service.  Propositions  have  often  been  made  to  substi- 
tute the  transverse  for  the  tensile  test  in  the  reception 
of  material.  These  suggestions  have  usually  been 


152  HYDRAULIC   CEMENT. 

based  upon  the  simplicity  of  the  test  and  of  the 
apparatus  with  which  it  may  be  carried  out.  All  that 
is  necessary,  after  the  bar  is  prepared,  is  the  arrange- 
ment of  a  couple  of  knife-edges  upon  which  the  ends 
of  the  bar  may  be  rested,  and  a  third  knife-edge  to 
carry  the  weight  brought  upon  the  middle  of  the  bar. 
The  ordinary  test  by  tension  is,  however,  quite  simple, 
and  there  seems  to  be  little  if  any  advantage  in  mak- 
ing a  change,  although  the  transverse  test  offers  an 
equally  effective  means  of  determining  quality.  Much 
less  is  known  as  to  what  the  transverse  strength  should 
be,  and  its  use  in  specifications  would  need  to  be  pre- 
ceded by  experiments  to  obtain  proper  values  for  the 
loads  to  be  required,  while  the  errors  due  to  differences 
in  making  briquettes  would  exist  the  same  in  the  one 
case  as  in  the  other. 

Prof.  Durand-Claye  made  a  large  number  of  tests  to 
compare  tensile  and  transverse  strength  for  both  neat 
cement  and  mortars  in  small  test-pieces.  He  used 
bars  2  centimeters  square  and  12  centimeters  long,  and 
tension-pieces  of  the  ordinary  5-square-centimeter  sec- 
tion, and  found  the  results  quite  regular.  The  modulus 
of  rupture  per  square  centimeter,  computed  by  the 

3  PI 
ordinary    formula    (R  = ,,    where  P  =  load,   /  = 

length,  and  a*  =  area),  were  found  to  average  a  little 
less  than  twice  the  unit  stress  for  tension.  The  use  of 
this  formula  in  this  instance  is  of  course  inexact,  as  it 
assumes  the  material  to  have  the  same  coefficient  of 
elasticity  for  tension  as  for  compression,  and  to  be 
strained  only  to  the  elastic  limit.  As  all  the  speci- 


TESTS   OF  THE   STRENGTH   OF   MORTAR 


153 


mens  are  of  the  same  size,  however,  this  is  immaterial 
for  purposes  of  comparison. 

In  making  the  transverse  test  the  most  common 
method  has  been  to  provide  supports  for  the  ends  of 
the  bar  and  hang  weights  directly  upon  its  middle. 
Care  should  be  exercised  to  guard  against  the  crushing 
of  the  material  under  the  knife-edges;  a  good  plan  is 
to  use  small  plates  of  iron  between  the  knife-edge 
and  the  surface  of  the  briquette  to  distribute  the  load. 

Where  a  tension-machine  is  in  use,  a  transverse 
attachment  is  readily  added,  by  which  both  tests  may 
be  made  by  the  same  machine.  Fig.  24  shows  such 


FIG.  24. 

an  attachment  as  it  is  commonly  used  in  Europe  in 
connection  with  the  Michaelis  machine;  the  rod  K  is 
attached  to  the  end  of  the  lower  lever  in  the  machine 
(Ay  Fig.  15),  thus  receiving  a  less  effect  from  the  ap- 
plication of  the  load  than  the  tension  specimen. 

ART.  50.     TESTS  OF  SAND-MORTAR. 

Tests  of  the  strength  of  sand-mortar,  although  com- 
monly recommended,  are  not  very  generally  employed 


154  HYDRAULIC   CEMENT. 

in  ordinary  specifications,  reliance  being  usually  placed 
upon  the  neat  test,  coupled  with  that  for  fineness,  to 
indicate  how  the  cement  will  act  when  mixed  with 
sand.  A  tensile  test  with  sand  is,  however,  of  the 
greatest  value  when  properly  conducted,  because  it 
accords  more  nearly  with  the  conditions  under  which 
the  cement  is  to  be  used. 

Tests  with  sand  may  be  made  either  as  a  means  of 
judging  the  value  of  the  cement,  or  to  determine  the 
probable  strength  of  mortar  under  the  circumstances 
which  may  obtain  in  special  work.  When  the  tests  are 
intended  as  a  determination  of  value,  it  is  essential 
that  they  be  made  according  to  some  standard  forming 
ready  means  of  comparison  with  other  material.  This 
requires  that  the  specimens  be  made  and  tested 
according  to  standard  methods,  and  that  the  sand  used 
be  of  standard  quality. 

In  the  German  specifications  the  standard  sand  is 
described  as  follows:  "  In  order  to  obtain  concordant 
results  in  the  tests,  sand  of  uniform  size  of  grain  and 
uniform  quality  must  be  used.  This  standard  sand  is 
obtained  by  washing  and  drying  the  purest  quartz 
sand  obtainable,  sifting  the  same  through  a  sieve  of 
60  meshes  per  square  centimeter,  thereby  separating 
the  coarsest  particles,  and  by  removing  from  the  sand 
so  obtained,  by  means  of  a  sieve  of  120  meshes  per 
square  centimeter,  the  finest  particles.  The  diameters 
for  the  wires  of  the  sieve  shall  be  0.38  millimeter  and 
0.32  millimeter  respectively."  The  German  Confer- 
ence upon  Uniform  Tests  specified  Freienwalde  sand 
as  the  standard. 

The  committee  of  the  American  Society  of  Civil 


TESTS   OF  THE   STRENGTH   OF   MORTAR.          155 

Engineers    recommend    an    artificial    sand    made    by 
crushing  quartz.     Their  report  is  as  follows: 

"  The  question  of  a  standard  sand  is  of  great  im- 
portance, for  it  has  been  found  that  sand  looking  alike 
and  sifted  through  the  same  sieve  gives  results  vary- 
ing within  rather  wide  limits. 

"  The  material  that  seems  likely  to  give  the  best 
results  is  the  crushed  quartz  used  in  the  manufacture 
of  sand-paper.  It  is  a  commercial  product,  made  in 
large  quantities  and  of  standard  grades,  and  can  be 
furnished  of  a  fairly  uniform  quality.  It  is  clean  and 
sharp,  and  although  the  present  price  is  somewhat 
excessive  (3  cents  per  pound),  it  is  believed  that  it  can 
be  furnished  in  quantity  for  about  $5.00  for  300  Ibs. 
As  it  would  be  used  for  tests  only,  for  purposes  of 
comparison  with  the  local  sands  and  with  tests  of 
different  cements,  not  much  of  it  would  be  required. 

"  The  price  of  German  standard  sand  is  about  $1.25 
for  112  Ibs. ;  but  the  article  being  washed,  river-sand 
is  probably  inferior  to  crushed  quartz.  Crushed 
granite  could  be  furnished  at  a  somewhat  less  rate  than 
crushed  quartz,  and  crushed  trap  for  about  the  same 
as  granite;  but  no  satisfactory  estimate  has  been 
obtained  for  either  of  these. 

"  The  use  of  crushed  quartz  is  recommended  by 
your  committee,  the  degree  of  fineness  to  be  such 
that  it  will  all  pass  a  No.  20  sieve  and  be  caught  on  a 
No.  30  sieve." 

This  sand  can  now  be  obtained  of  dealers  in  testing 
apparatus,  but  much  of  what  is  furnished  for  the  pur- 
pose requires  resifting  to  bring  it  to  standard  size. 
The  use  of  this  sand  is  probably  advantageous  as  con- 


I $6  HYDRAULIC   CEMENT. 

ducing  to  uniformity,  but  it  gives  less  strength  in 
mortar  than  good  natural  sand. 

In  France  both  artificial  sand  (crushed  quartz)  and 
natural  sand  are  used  to  some  extent  in  tests.  The 
Commission  on  Methods  of  Testing  recommend  the 
use  of  natural  sand.  They  divide  the  sand  into  these 
sizes: 

i.  Sand  which  passes  openings  of  i  mm.  and  is 
retained  by  those  of  0.5  mm.  2.  Sand  which  passes 
openings  of  1.5  mm.  and  is  retained  by  those  of  i.o 
mm.  3.  Sand  which  passes  openings  of  2.0  mm.  and 
is  retained  by  those  of  1.5  mm. 

The  name  simple  standard  sand is  given  to  No.  2, 
and  the  name  compound  standard  sand  to  a  mixture  of 
equal  parts  of  the  three  sizes.  The  former  is  to  be 
used  in  making  mortar  for  standard  tests  where  the  dry 
consistency  is  employed,  and  the  briquettes  made  by 
pounding.  The  latter  is  required  in  gauging  when 
the  plastic  consistency  is  used. 

Tests  of  sand-mortar  for  the  purpose  of  comparing 
various  sands  with  the  standard  sand,  or  of  estimating 
the  efficiency  of  mortar  under  varying  circumstances 
of  use,  are  often  of  much  value  as  a  guide  to  the 
proper  use  of  the  material.  In  such  work  the  method 
of  testing  necessarily  depends  upon  the  point  to  be 
investigated. 

ART.  51.     INTERPRETATION  OF  RESULTS. 

The  test  for  strength  is  regarded  as  a  measure  of 
the  value  of  a  cement,  as  showing  the  possession  of 
the  active  elements.  There  are,  however,  different 


TESTS   OF  THE   STRENGTH   OF   MORTAR.          1 57 

elements  which  act  at  different  rates,  and  it  is  unwise 
to  classify  cements  according  to  strength  alone.  The 
tensile  strength  developed  by  cement  in  a  test  extend- 
ing over  a  short  period  of  time  is  not  necessarily  an 
indication  of  the  strength  that  may  be  attained  by  it 
during  a  longer  period,  unless  the  normal  action  of  the 
particular  material  be  known.  That  which  is  strongest 
at  first  may  not  continue  to  be  the  strongest. 

The  development  of  good  strength  soon  after  the 
use  of  the  mortar  is  a  desirable  attribute  in  most 
engineering  work,  and  the  probability  of  the  material 
being  good  is  greater  where  it  shows  a  fair  early 
strength,  and  therefore  it  is  usually  wise  to  specify 
that  the  cement  shall  develop  a  fairly  good  strength 
on  a  short-time  test,  but  there  is  no  object  in  requir- 
ing extremely  high  values. 

Mr.  Faija  recommends  that  the  gain  in  strength 
between  the  7  and  28  day  periods  be  considered, 
rather  than  the  absolute  early  strength,  in  determining 
the  probable  subsequent  gain  in  strength.  This  is 
doubtless  a  better  guide  than  the  usual  one,  but  it  is 
not  usually  practicable  to  require  tests  extending  over 
a  period  of  28  days,  and  in  many  instances  it  would 
be  misleading,  if  comparison  of  different  cements  were 
attempted. 

Prof.  Unwin  gives  a  formula  for  the  strength  at  any 
period,  y  =  a  -f-  b(x  —  i)",  in  which  y  is  the  strength 
at  x  weeks  after  mixing;  a,  the  strength  at  end  of  one 
week;  n,  a  constant  for  the  particular  material,  to  be 
determined  by  observations  extending  over  consider- 
able time;  b,  a  constant  to  be  determined  from  the 
strengths  given  by  the  sample  at  I  week  and  4  weeks 


158  HYDRAULIC  CEMENT. 

after  mixing.  Prof.  Unwin  gives  the  value  n  =  1/3  for 
Portland  cement  in  general,  and  shows  that  the  formula 
gives  values  well  in  accord  with  the  results  of  tests  in 
many  instances.  The  formula  depends  upon  the 
assumption  that  for  any  two  Portland  cements  the 
gains  in  strength  at  end  of  any  period  are  to  each  other 
as  the  gains  between  the  7  and  28  day  test, — a  propo- 
sition quite  wide  of  the  mark  in  many  instances. 

The  strengths  commonly  required  by  specifications, 
in  the  United  States,  are  based  upon  the  recommen- 
dations of  the  committee  of  the  American  Society  of 
Civil  Engineers,  which  gives  the  following  average 
values: 

'  American  Natural  Cement,  Neat. 

I  day,  I  hour  or  until  set  in  air,  the  rest  of  the  24 
hours  in  water,  from  40  to  80  Ibs. 

i  week,  i  day  in  air,  6  days  in  water,  from  60  to 
100  Ibs. 

I  month,  i  day  in  air,  27  days  in  water,  from  100 
to  150  Ibs. 

i  year,  i  day  in  air,  remainder  in  water,  from  300 
to  400  Ibs. 

American  and  Foreign  Portland  Cements,  Neat. 
day,  i  hour  or  until  set  in  air,  the  rest  of  the  24 
hours  in  water,  from  100  to  140  Ibs. 

i  week,  i  day  in  air,  6  days  in  water,  from  250  to 
550  Ibs. 

i  month,  i  day  in  air,  27  days  in  water,  from  350 
to  700  Ibs. 

i  year,  i  day  in  air,  remainder  in  water,  from  450 
to  800  Ibs. 


TESTS   OF  THE  STRENGTH  OF  MORTAR.          159 

American  Natural  Cements,  I  part  Cement  to  I  part 
of  Sand. 

i  week,  i  day  in  air,  6  days  in  water,  from  30  to 
50  Ibs. 

i  month,  I  day  in  air,  27  days  in  water,  from  50  to 
80  Ibs. 

i  year,  i  day  in  air,  remainder  in  water,  from  200 
to  300  Ibs. 

American  and  Foreign  Portland  Cements,    I  part  of 
Cement  to  3  parts  of  Sand. 

i  week,  i  day  in  air,  6  days  in  water,  from  80  to 
125  Ibs. 

i  month,  i  day  in  air,  27  days  in  water,  from  100 
to  250  Ibs. 

i  year,  i  day  in  air,  remainder  in  water,  from  200 
to  350  Ibs." 

At  least  the  minimum  value  here  given  for  i  and  7 
days  are  usually  required  in  ordinary  specifications, 
but  higher  values  are  often  employed.  Many  of  the 
better  cements  commonly  give  results  above  the  maxi- 
mum values  stated  above;  this  depends,  however, 
upon  how  they  are  tested. 

The  values  to  be  required  in  specifications  need  to 
be  modified,  especially  with  the  natural  cements,  to 
accord  with  the  particular  kind  of  cement  to  be  used, 
and  also  with  the  practice  of  the  laboratory. 

Where  large  quantities  of  cement  are  regularly  em- 
ployed, and  the  same  men  continuously  make  the  tests, 
it  is  a  comparatively  simple  matter  to  conform  the 
specifications  to  the  work  of  the  laboratory  so  as  to 


l6o  HYDRAULIC  CEMENT. 

get  reliable  indications  of  the  value  of  the  material. 
A  very  large  portion  of  the  testing  for  reception  of 
material  must,  however,  be  done  upon  detached  works, 
where  temporary  laboratories  are  to  be  used,  and  in- 
spectors employed  for  the  occasion.  In  these  cases 
it  is  a  difficult  matter  to  adopt  a  specification  which 
shall  give  good  results,  unless  the  operator  can  himself 
first  be  calibrated. 

The  results  of  tests  in  the  permanent  laboratories 
usually  give  higher  strength  for  the  same  material  than 
would  be  obtained  on  an  ordinary  outside  test,  espe- 
cially by  a  comparatively  inexperienced  man.  It  is 
not  to  be  inferred,  however,  that  the  highest  results 
are  necessarily  the  outcome  of  the  greatest  skill.  As 
a  rule,  the  most  expert  and  reliable  operators  get  only 
moderate  strength  for  the  best  material. 

Lack  of  skill  in  conducting  tests  nearly  always  tells 
against  the  material  tested,  and  good  material  may 
often  be  rejected  because  of  inexperience  in  the  in- 
spector; but,  on  the  other  hand,  it  is  a  frequent  trick 
of  contractors  having  inferior  material  rejected  on  an 
ordinary  test  to  send  it  to  one  of  the  laboratories 
known  to  obtain  abnormally  high  strengths,  and  thus 
get  results  which  seem  to  show  error  on  the  original 
test. 

In  specifications  it  is  usually  desirable  to  require 
tests  showing  a  fair  degree  of  strength  rather  than  very 
high  values.  The  latter  are  if  anything  less  likely  to 
give  good  material  and  unnecessarily  limit  competi- 
tion. 


CHAPTER   VII. 
TESTS   FOR   SOUNDNESS. 

ART.  52      ORDINARY  TESTS. 

SOUNDNESS  is  the  most  important  quality  of  a 
cement,  as  it  means  the  power  of  the  cement  to  resist 
the  disintegrating  influences  of  the  atmosphere  or 
water  in  which  it  may  be  placed.  Unsoundness  in 
cement  may  vary  greatly  in  degree,  and  show  itself 
quite  differently  in  different  material.  Cement  in 
which  the  unsoundness  is  very  pronounced  is  apt  to 
become  distorted  and  cracked  after  a  few  days,  when 
small  cakes  are  placed  in  water.  Those  in  which  the 
disintegrating  action  is  slower  may  not  show  any  visi- 
ble change  of  form,  but  after  weeks  or  months 
gradually  lose  coherence,  and  soften  until  entirely 
disintegrated. 

The  method  in  common  use  for  testing  unsoundness 
is  to  make  small  cakes  or  pats  of  neat  cement,  usually 
about  3  or  4  inches  in  diameter  and  1/2  inch  thick, 
upon  a  plate  of  glass,  and  keep  them  in  air  or  water 
for  a  few  days,  carefully  watching  them  to  see  if  they 
show  any  signs  of  distortion  or  surface  cracks,  which 
may  indicate  a  tendency  to  disintegration. 

The  German  standard  specifications  require  that  the 

161 


162  HYDRAULIC   CEMENT. 

cakes  for  this  test  shall  be  1.5  centimeters  thick  at  the 
centre  and  have  thin  edges.  These  cakes  are  placed  in 
water  24  hours  after  they  are  made,  or  at  least  not 
until  they  are  firmly  set,  and  observations  are  con- 
tinued over  a  period  of  28  days,  when,  if  no  cracks  or 
distortions  appear,  the  cement  is  considered  sound. 

"  The  cakes,  especially  those  of  slow-setting  cement, 
must  be  protected  against  draughts  and  sunshine  until 
their  final  setting.  This  is  best  accomplished  by  keep- 
ing them  in  a  covered  box  lined  with  zinc  or  under 
wet  cloths.  In  this  manner  the  formation  of  heat 
cracks  is  avoided,  which  are  generally  formed  in  the 
centre  of  the  cake,  and  may  be  taken  by  an  inexperi- 
enced person  for  cracks  formed  by  blowing." 

The  Committee  of  the  American  Society  of  Civil 
Engineers  recommend  the  following: 

"Make  two  cakes  of  neat  cement  two  or  three  inches 
in  diameter,  about  one  half  inch  thick,  with  thin  edges. 
Note  the  time  in  minutes  that  these  cakes,  when 
mixed  with  water  to  the  consistency  of  a  stiff  plastic 
mortar,  take  to  set  hard  enough  to  stand  the  wire  test 
recommended  by  General  Gillmore,  i/12-inch  diam- 
eter wire  loaded  with  one  fourth  of  a  pound,  and 
i/24-inch  loaded  with  one  pound. 

"  One  of  these  cakes,  when  hard  enough,  should  be 
put  in  water  and  examined  from  day  to  day  to  see  if 
it  becomes  contorted,  or  if  cracks  show  themselves  at 
the  edges,  such  contortions  or  cracks  indicating  that 
the  cement  is  unfit  for  use  at  that  time.  In  some 
cases  the  tendency  to  crack,  if  due  to  free  lime,  will 
disappear  with  age.  The  remaining  cake  should  be 
kept  in  the  air  and  its  color  observed,  which  for  a 


TESTS   FOR   SOUNDNESS.  163 

good  cement  should  be  uniform  throughout,  yellowish 
blotches  indicating  a  poor  quality  the  Portland 
cements  being  of  a  bluish  gray  and  the  natural  cements 
being  dark  or  light,  according  to  the  character  of  the 
rock  of  which  they  are  made.  The  color  of  the 
cements  when  left  in  the  air  indicates  the  quality  much 
better  than  when  they  are  put  in  water." 

The  color  test  above  given  is  not  of  much  value,  as 
unsound  cement  is  very  commonly  of  good  color. 
The  time  during  which  these  observations  shall  con- 
tinue is  not  specified  in  these  rules,  but  in  practice 
they  are  not  usually  carried  over  more  than  two  days 
to  a  week  before  acceptance  of  the  material. 

The  French  Commission  upon  Methods  of  Testing 
Materials  recommend  both  a  pat  test  and  test  of  the 
amount  of  swelling  which  takes  place  in  the  mortar, 
as  follows: 

"  Cold  Tests. — (a)  For  this  test  the  cement  paste 
is  formed  into  a  pat  about  10  centimeters  in  diameter 
and  2  centimeters  thick,  made  thin  at  the  edges. 

"  Immediately  after  being  made  the  specimens  in- 
tended for  tests  in  water  are  immersed  in  the  same 
conditions  as  the  briquettes  used  for  tensile  tests. 

"  The  specimens  intended  for  use  in  the  air  are  at 
once  exposed  to  the  conditions  indicated  for  bri- 
quettes." 

"  The  condition  of  the  specimens  is  observed  at  the 
same  periods  of  time  employed  in  making  tensile  tests 
(7  days,  28  days,  3  months,  6  months,  I  year,  etc.). 

"  (b)  To  measure  the  increase  in  volume  of  the 
mortar  of  neat  cement  after  prolonged  immersion  in 
cold  water,  a  bar  of  cement  is  employed  80  centi- 


164  HYDRAULIC   CEMENT. 

meters  in  length  and  12  millimeters  square,  placed 
vertically  in  a  glass  tube  25  millimeters  in  diameter, 
which  is  then  filled  with  water. " 

"  The  elongation  is  measured  by  the  motion  upon 
an  arc  of  a  needle  moved  by  a  rod  resting  upon  the 
upper  extremity  of  the  bar  of  mortar."  (See  Fig.  25.) 

The  method  of  testing  by  measuring  the  variation 
in  length  is  also  used  to  some  extent  in  Germany. 
Methods  of  conducting  this  test  are  described  in  Art. 

53- 

It  is  important  in  testing  soundness  in  this  manner 
that  the  tests  should  be  continued  over  as  long  a 
period  as  possible,  and  many  cases  of  unsoundness  are 
not  discovered  with  a  28-day  test.  Instances  have 
been  observed  in  which  mortar  in  the  form  of  2-inch 
cubes  has  completely  disintegrated  within  two  years, 
where  incipient  checking  was  not  observable  for  three 
months  in  a  small  cake  test.  The  most  common  and 
dangerous  cases  of  unsoundness  are  probably  discov- 
ered by  the  ordinary  tests.  It  may  be  observed,  how- 
ever, that  the  fact  that  disintegration  of  mortar  is  not 
oftener  observed  in  large  constructions  is  probably  due 
more  to  the  general  good  quality  of  the  cement  sup- 
plied by  the  best  makers,  and  to  the  frequent  stability 
of  work  regardless  of  the  nature  of  the  mortar,  than 
to  the  efficiency  of  the  test  for  soundness. 

The  quantity  of  water  to  be  used  in  mixing  mortar 
for  tests  of  soundness  is  about  the  same  as  that  used 
for  tests  of  strength,  although  a  variation  in  the  quan- 
tity, within  small  limits,  does  not  seem  to  materially 
influence  the  results.  Care  must  be  taken  that  the 
cakes  be  kept  moist  during  setting  and  previous  10 


TESTS   FOR  SOUNDNESS.  165 

immersion,  in  order  that  they  may  be  free  from  dry- 
ing cracks.  On  this  account  the  French  commission 
consider  it  preferable  to  immerse  the  specimens  im- 
mediately after  mixing,  without  waiting  for  the  mor- 
tar to  set.  Some  natural  cements  do  not  stand  imme- 
diate immersion  although  apparently  quite  sound  in 
water  if  first  allowed  to  set  in  air. 

When  mortar  is  to  be  used  in  sea-water,  the  pats  of 
cement  are  placed  in  water  of  the  same  character,  and 
as  nearly  as  possible  corresponding  to  the  conditions 
of  practice. 

Practically,  however,  the  action  of  sea-water  is  so 
slow  that  the  test  is  comparatively  useless.  M.  Alex- 
andre  found  *  that  the  first  indication  of  disintegration 
may  not  be  shown  for  several  months  or  perhaps 
years.  He  also  found  that  the  action  in  the  labora- 
tory did  not  always  accord  with  that  in  the  work. 
This  was  probably  due  to  failures  occurring  because  of 
the  method  of  employing  the  mortar,  when  the  cement 
was  not  defective. 

Tests  are  sometimes  made  of  mortar  to  be  used  in 
sea-water  by  causing  the  water  to  filter  through  the 
block  of  mortar  under  pressure.  This  test  is  made 
in  France  by  employing  the  standard  cubes  used  in 
compression,  which  are  arranged  and  submitted  to 
filtration  as  in  the  tests  for  permeability  (see  Art.  67). 
These  blocks  are  afterward  crushed,  and  their  strengths 
compared  with  those  kept  under  normal  conditions. 

*Annales  des  Fonts  et  Chaussees,  Sept.  1890,  p.  131. 


l66  flYDRAULIC   CEMENT. 


ART.  53.     MEASUREMENT  OF  EXPANSION. 

Unsoundness  in  cement  is  doubtless  for  the  most 
part  due  to  the  presence  of  expansive  elements,  the 
action  of  which  subsequent  to  the  setting  of  the 
cement  produces  internal  forces,  tending  to  disrupt 
the  mass  of  mortar  and  usually  causing  an  increase  in 
its  volume.  The  various  tests  for  soundness  have  for 
their  object  the  determination  of  the  presence  of 
these  expansives,  which  may  be  indicated  either  by 
the  distortion  and  cracking  of  the  mortar  when 
present  in  sufficient  quantity,  or  by  a  simple  increase 
in  volume  without  visible  distortion  when  present  in 
less  quantity,  or  when  more  finely  divided  and  uni- 
formly distributed  through  the  mass. 

As  a  more  efficient  and  accurate  method  of  deter- 
mining the  presence  of  expansives  than  is  afforded  by 
the  observation  of  thin  pats  of  mortar,  various  appli- 
ances have  been  devised  for  the  purpose  of  measuring 
directly  the  increase  of  volume  of  a  block  of  mortar. 

The  Long-bar  Apparatus. — The  first  apparatus  for 
the  purpose  of  measuring  change  of  dimensions  was 
devised  by  MM.  Durand-Claye  and  Debray.  It  has 
been  in  use  for  a  number  of  years  in  France,  and  was 
recommended  for  use  in  cold  tests  by  the  French 
Commission  on  Methods  of  Testing  Materials  (see  Art. 
52).  This  apparatus  is  shown  in  Fig.  25.  The  test 
is  made  upon  bars  80  centimeters  long  and  12  millim- 
eters square  in  section.  The  moulds  in  which  these 
bars  are  formed  consist  of  iron  rods  considerably  longer 
than  the  bars  to  be  formed,  and  of  section  30  by  12 


TESTS   FOR   SOUNDNESS. 


I67 


millimeters,  laid  flat  upon  a  table,  held  apart  at  the 
ends  by  blocks  of  the  same  section  as  the  cement  bar. 
and  prevented  from  spreading  by  clamps  at  the  ends. 
In  making  the  test,  the  bar  of  cement  is  placed  in  a 
vertical  glass  tube  80  centimeters  long  and  23  nui 


FIG.  25. 

limeters  in  diameter,  closed  at  the  bottom  and  rilled 
with  the  water,  to  the  action  of  which  the  mortar  is  to 
be  exposed.  To  the  top  of  the  glass  tube  is  fixed  a 
ring  carrying  on  one  side  an  arc  and  on  the  other  a 
rod,  to  which  is  hinged  a  needle,  which  travels  upon 
the  arc,  being  actuated  by  a  rod  resting  upon  the  top 
of  the  cement  bar.  The  extension  of  the  cement  bar 
is  thus  multiplied  by  10  in  the  reading  on  the  arc, 
which  may  be  graduated,  and  the  successive  positions 


i68 


HYDRAULIC   CEMENT. 


of  the  needle  read  from  the  scale,  or  it  may  be  covered 
with  blank  paper,  and  have  the  positions  of  the  needle- 
point marked  and  afterward  measured.  This  method 
requires  much  care  in  manipulation,  both  in  making 
the  bars  and  in  handling  them  in  the  test. 

Bauschinger 's  Caliper  Apparatus. — This  apparatus, 
designed  by  Prof.  Bauschinger  and  used  in  the  German 


FIG.  26. 


ard  Swiss  laboratories,  is  an  arrangement  for  measur- 
ing the  change  of  length  of  a  short  bar.  It  is  shown 
in  Fig.  26. 


TESTS   FOR   SOUNDNESS.  169 

The  bars  used  in  the  test  are  about  100  millimeters 
in  length  and  5  square  centimeters  in  section. 

They  are  moulded  with  square  cavities  in  the  ends 
of  the  bars,  in  which  are  set  small  plates  containing 
centres,  to  form  bearings  for  the  points  of  the  microm- 
eter-screw. The  change  in  length  may  be  measured 
to  1/200  millimeter. 

The  measuring  apparatus  is  suspended  by  a  rod  from 
a  bar  pivoted  upon  the  top  of  the  standard  and 
balanced  by  counterweights  so  as  to  hang  level.  It 
consists  of  the  caliper  bar  A,  one  end  of  which  carries 
a  micrometer-screw,  reading  to  1/200  millimeter,  and 
the  other  end,  a  vertical  bar  to  the  bottom  of  which 
is  hinged  the  needle  D.  The  lower  end  of  the  needle 
has  a  point  which  is  pressed  by  a  spring  against  the 
end  of  the  specimen  in  taking  a  measurement.  The 
pressure  of  the  micrometer  against  the  specimen  is 
regulated  by  bringing  the  point  of  the  needle  to  zero 
on  the  scale  F.  A  small  bar  of  metal  encased  in 
wood  is  used  as  a  standard  in  calibrating  the  instru- 
ment, the  length  of  the  standard  being  known  very 
accurately  at  a  definite  temperature. 

Le  Chatelier's  Apparatus. — The  apparatus  of  Prof. 
Le  Chatelier  is  designed  to  measure  the  increase  in 
circumference  of  a  cylindrical  block  of  mortar.  This 
method  is  recommended  by  the  French  commission 
for  use  in  making  hot  tests,  and  is  said  to  have  the 
advantage  of  being  much  more  easily  manipulated 
than  the  other  methods.  It  has  also  been  suggested 
that  the  increase  in  length  for  long  bars  may  not  be 
an  accurate  indication  of  the  actual  swelling,  as  there 
would  be  a  tendency  for  the  expansion  to  take  lines 


170  HYDRAULIC  CEMENT. 

of  least  resistance,  and  therefore  the  transverse  swell- 
ing may  be  more  than  the  longitudinal. 

This  apparatus  is  shown  in  Fig.  27.  It  is  described 
by  Prof.  Le  Chatelier  as  follows:*  "A  much  more 
simple  and  yet  sufficiently  precise  measurement  of  the 
expansion  can  be  made  by  letting  the  cement  harden 
in  cylindrical  moulds  of  a  diameter  equal  to  their 


FIG.  27. 

height  (for  example  30  mm.),  constructed  of  metal 
0.5  mm.  thick,  slit  along  generatrix  and  provided  on 
each  side  of  the  slit  with  two  long  needles  (150  mm. 
for  example),  which  serve  to  magnify  any  widening  of 
'the  slit.  The  widening  is  equal  to  the  enlargement, 
not  of  the  diameter,  but  of  the  circumference  of  the 
cylinder  of  cement.  Very  slow-setting  cements  or 
limes,  the  water  of  which  would  evaporate  or  drain 
away  in  air,  it  is  indispensable  to  immerse  as  soon  as 
moulded,  without  waiting  for  them  to  set.  The  im- 
mersion in  water  of  a  porous  mass  filled  with  air  may 
sometimes,  by  reason  of  capillary  phenomena,  give 
rise  to  a  certain  expansion,  and  even  to  more  or  less 
disintegration,  if  the  hardness  be  insufficient.  During 
the  moulding  and  until  the  setting  has  taken  place 
the  mould  should  be  kept  firm  by  means  of  a  suitable 
holder,  which  is  removed  after  setting  and  before  the 
measurements  are  begun." 

*  Trans.  Am.  Inst.  Mining  Eng. 


TESTS   FOR   SOUNDNESS.  17 1 

"  For  products  of  good  quality,  the  distance  be- 
tween the  points  of  the  needles  does  not  attain  I  mm. 
in  28  days  from  the  time  of  the  end  of  setting.  This 
test  for  invariability  of  volume,  when  made  cold,  has 
but  little  interest,  since  it  detects  only  exceptionably 
bad  products." 

ART.  54.     ACCELERATED  TESTS. 

The  fact  that  many  cases  of  unsoundness  in  cement 
are  not  shown  by  the  ordinary  tests  when  extended 
over  a  short  period  of  time  has  long  been  recognized, 
and  many  efforts  have  been  made  to  find  some  means 
of  determining  with  accuracy  and  within  a  reasonable 
time  whether  the  material  be  reliable.  The  difficulty 
of  this  with  a  material  of  so  variable  a  nature,  and  in 
which  failure  may  be  due  to  so  many  and  so  diverse 
causes,  is  self-evident.  Each  test  must  be  directed  to 
the  determination  of  the  presence  of  some  particular 
cause  of  unsoundness,  and  all  of  them  seem,  when 
indiscriminately  applied  to  all  cements,  to  meet 
material  which  will  not  pass  them,  although  of  good 
quality,  and  to  which  they  are  evidently  inapplicable. 

Nearly  all  of  these  tests  are  directed  to  the  detec- 
tion of  the  so-called  expansives,  and  most  of  them 
attempt  to  accelerate  the  chemical  action,  which 
causes  the  swelling  and  disintegration,  by  the  action 
of  heat.  Some  of  the  heat  tests  have  proven  fairly 
successful  in  use,  although  none  have  been  exten- 
sively employed  as  tests  for  the  reception  of  material. 

Hot  tests  were  first  suggested  by  Dr.  Michaelis,  who 
proposed  the  use  of  heat  to  advance  the  hardening  of 


172  HYDRAULIC  CEMENT. 

cement,  with  a  view  to  determining,  from  the  strength 
gained  in  a  short  time  in  hot  water,  that  which  would 
result  in  a  longer  period  under  normal  conditions. 
From  the  first  experiments  in  this  direction  it  ap- 
peared that  the  results  obtained  in  from  I  to  7  days 
in  hot  water  might  bear  a  definite  relation  to  those 
obtained  in  much  longer  periods  at  ordinary  tempera- 
tures. Later  experiments  showed,  however,  that 
while  this  might  be  true  of  a  limited  class  of  materials, 
as  the  composition  is  varied  the  effect  of  heat  upon 
the  strength  also  varies  in  a  marked  degree,  some 
cement  even  showing  a  loss  of  strength  in  hot  as  com- 
pared with  cold  water. 

In  a  series  of  tests  made  by  M.  Deval  it  was  found 
that  the  addition  of  a  small  percentage  of  quicklime 
to  a  good  Portland  cement  caused  the  cement  to 
attain  less  strength  when  kept  in  hot  than  in  cold 
water,  and  Prof.  Le  Chatelier  proposed  to  utilize  this 
discovery  for  detecting  the  presence  of  free  lime. 
He  suggested  the  use  of  briquettes  of  I  to  3  mortar, 
and  the  comparison  of  the  strengths  of  briquettes 
conserved  for  3  and  7  days  in  water  at  80°  C  with 
those  kept  for  7  and  28  days  in  water  at  ordinary 
temperatures;  the  cements  of  good  quality  to  show  a 
strength  at  least  equal  in  hot  to  that  attained  in  cold 
water. 

It  is  to  be  observed  in  considering  this  test  that 
there  are  some  good  cements  which  give  less  strength 
hot  than  cold  when  of  normal  quality.  M.  Alexandre 
found  that  cements  rich  in  aluminates  behave  in  this 
manner.  There  are  also  certain  cements  which  give 
high  tests  in  hot  water  notwithstanding  the  presence 


TESTS   FOR   SOUNDNESS.  1/3 

of  appreciable  quantities  of  expansives.  These  are 
apparently  siiicious  cements  of  low  hydraulic  index, 
in  which  the  free  lime  while  rendering  the  cement 
unsound  does  not  cause  it  to  lose  strength  in  hot 
water  during  the  short  period  of  the  test. 

There  are  several  methods  of  testing  the  soundness 
of  cement  by  the  aid  of  heat,  which  have  come  more 
or  less  into  use,  and  have  in  many  instances  given 
satisfactory  results.  These  all  aim  at  the  detection 
of  the  presence  of  expansives  through  accelerating 
their  action  by  heat,  and  then  observing  the  deforma- 
tions or  measuring  the  expansion  as  in  the  correspond- 
ing cold  tests.  Descriptions  of  these  tests  are  given 
in  the  following  articles. 

ART.  55.     KILN  TEST. 

This  test  was  originated  by  Dr.  Bohme,  and  consists 
in  exposing  small  cakes  of  the  cement  to  heat  in  a 
drying  oven  for  a  definite  period,  and  observing 
whether  it  cracks. 

The  specifications  of  the  Association  of  German 
Cement  Makers  recommend  this  test  as  a  means  of 
forming  an  opinion  quickly,  but  make  the  ordinary  28- 
day  test  decisive  as  to  those  cements  which  fail  to 
pass  the  kiln  test.  In  these  specifications  the  kiln 
test  is  described  as  follows: 

"  For  making  the  heat  test,  a  stiff  paste  of  neat 
cement  and  water  is  made,  and  from  this  cakes  8  cm. 
to  10  cm.  in  diameter  and  i  cm.  thick  are  formed  on 
a  smooth  impermeable  plate  covered  with  blotting- 
paper.  Two  of  these  cakes,  which  are  to  be  protected 


174  HYDRAULIC   CEMENT. 

against  drying,  in  order  to  prevent  drying  cracks,  are 
placed,  after  the  lapse  of  twenty-four  hours,  or  at 
least  only  after  they  have  set,  with  their  smooth  sur- 
faces on  a  metal  plate  and  exposed  for  at  least  one 
hour  to  a  temperature  of  from  1 10°  C.  to  120°  C., 
until  no  more  water  escapes.  For  this  purpose  the 
drying  closets  in  use  in  chemical  laboratories  may  be 
utilized.  If  after  this  treatment  the  cakes  show  no 
edge  cracks,  the  cement  is  to  be  considered  in  general 
of  constant  volume.  If  such  cracks  do  appear,  the 
cement  is  not  to  be  condemned ;  but  the  results  of  the 
decisive  test  with  the  cakes  hardening  on  glass  plates 
under  water  must  be  waited  for.  It  must,  however, 
be  noticed  that  the  heat  test  does  not  admit  of  a  final 
conclusion  as  to  the  constancy  of  volume  of  those 
cements  which  contain  more  than  3$  of  calcium  sul- 
phate (gypsum)  or  other  sulphur  combinations." 

This  test  is  considered  by  some  authorities  to  be  of 
value  for  cements  to  be  used  in  the  air.  It  differs 
very  radically,  however,  from  the  way  the  material  is 
used  in  practice,  as  it  effects  the  complete  drying  out 
of  the  mortar.  In  many  instances  also  it  is  very  diffi- 
cult to  interpret,  in  consequence  of  the  loss  of  cohe- 
sive strength  due  to  drying,  where  no  distortions 
appear.  The  effect  of  the  withdrawal  of  the  water 
necessary  to  the  proper  hardening  of  the  mortar  may 
vary  as  the  rapidity  of  action  of  the  material  varies. 

The  kiln  test  has  sometimes  been  modified  by  using 
a  moist  atmosphere  in  place  of  dry  air.  A  pan  of 
water  is  placed  in  the  oven  under  the  specimens;  the 
evaporation  serving  to  keep  the  air  saturated  with 
moisture.  Prof.  Tetmajer  used  this  method  in  a 


TESTS   FOR   SOUNDNESS.  I?5 

series  of  comparative  tests  and  found  it  to  give  results 
similar  to  those  of  his  boiling  test,  but  somewhat  less 
effective.  His  method  was  as  follows:  "  The  speci- 
mens are  placed  on  a  support  in  the  oven,  on  the 
bottom  of  which  are  several  millimeters  of  water. 
The  heat  is  gradually  applied  so  as  to  evaporate  all 
the  water  in  three  to  six  hours, — first  that  which  is  on 
the  bottom  of  the  oven,  then  that  which  has  been 
absorbed  by  the  mortar.  Until  the  water  is  entirely 
evaporated  the  temperature  remains  at  about  95°  C. 
The  heating  is  continued  a  half-hour  after  the  dis- 
engagement of  the  vapor  ceases,  in  such  manner  as  to 
raise  the  temperature  in  the  oven  to  12.0°  C.  Under 
these  conditions  the  interior  of  the  briquette  will 
reach  but  little  above  100°  C." 

"  It  should  be  remarked  that  by  this  method  it  is 
difficult  to  render  the  results  comparable.  It  is  not 
possible  to  make  the  duration  of  heat  exactly  the  same 
for  all  the  specimens,  and  after  the  evaporation  of  the 
water  the  heat  in  the  bottom  is  much  greater  than  at 
the  top  of  the  oven." 

Flame  Test.  —A  dry  heat  test  has  been  proposed, 
and  is  sometimes  made  in  Europe,  by  making  a  ball 
of  the  cement  paste  about  two  inches  in  diameter  and 
placing  it  on  a  gauze  in  the  flame  of  a  gas-jet.  The 
heat  is  gradually  applied,  so  that  at  the  end  of  an  hour 
it  reaches  a  temperature  of  about  90°  C.  The  heat 
is  then  increased  until  the  lower  part  of  the  ball 
becomes  red-hot,  after  which  it  is  cooled  and  examined 
for  cracks.  The  results  of  this  test  are  much  like 
those  of  the  dry-kiln  test,  and  are  usually  difficult  to 
interpret  satisfactorily. 


176  HYDRAULIC   CEMENT 


ART.  56.     STEAM  AND  HOT-WATER  TEST. 

This  test  consists  in  subjecting  cakes  of  cement, 
prepared  in  the  ordinary  manner,  to  the  action  of 
steam  for  three  or  four  hours,  then  immersing  in  hot 
water  for  the  remainder  of  twenty-four  hours,  and 
examining  for  cracks  and  distortions. 

Mr.  Faija,  by  whom  this  test  was  devised,  uses  it 
in  his  specifications  for  cement  in  England.  He 
describes  his  method  of  conducting  the  test  as  follows: 

"  Briefly,  it  is  a  vessel  containing  water,  the  water 
being  maintained  at  an  even  temperature  of  about 
1 10°  to  115°  Fahr. ;  there  is  a  cover  to  the  vessel,  so 
that  above  the  water  there  is  a  moist  atmosphere 
which  has  a  temperature  of  about  100°  Fahr.  The 
manner  of  carrying  out  the  test  is  by  making  a  pat, 
in  the  manner  already  described,  on  a  small  piece  of 
glass;  immediately  the  pat  is  gauged,  it  is  placed  on 
a  rack  in  the  upper  part  of  the  vessel,  and  is  there 
acted  upon  by  the  warm  vapor  rising  from  the  hot 
water;  when  the  pat  is  set  quite  hard,  it  is  taken  off 
the  rack  and  put  bodily  into  the  water,  which,  as  has 
been  already  stated,  is  maintained  at  a  temperature 
of  100°  to  115°  Fahr.,  and  in  the  course  of  twenty-four 
hours  it  is  taken  out  and  examined,  and  if  found  then 
to  be  quite  hard  and  firmly  attached  to  the  glass,  the 
cement  may  be  at  once  pronounced  sound  and  perfectly 
safe  to  use;  if,  however,  the  pat  has  come  off  the 
glass  and  shows  cracks  or  friability  on  the  edges,  or  is 
much  curved  on  the  under  side,  it  may  at  once  be 


TESTS  FOR  SOUNDNESS.  177 

decided  that  the  cement  in  its  present  condition  is  not 
fit  for  use." 

Mr.  Faija  prefers  the  temperature  given  above,  but 
other  experimenters  have  seemed  to  get  better  re- 
sults using  a  higher  one.  Prof.  Tetmajer  obtained 
fairly  good  results  with  a  temperature  just  below  the 
boiling-point — about  200°  Fahr.  He  subjected  the 
cakes  to  the  action  of  steam  for  four  hours,  and  hot 
water  twenty  hours,  placing  the  cakes  in  the  steam  as 
soon  as  mixed. 

Mr.  Maclay  modified  this  method  of  testing,  and 
introduced  it  into  the  specifications  of  the  Depart- 
ment of  Docks,  New  York  City.  Four  pats  or  cakes 
of  cement  prepared  in  the  usual  manner  were  used  by 
Mr.  Maclay  for  his  tests,  the  conduct  of  which  he 
describes  as  follows:*  "  One  of  these  pats  is  placed 
in  a  steam-bath,  temperature  195°  to  200°  Fahr.,  as 
soon  as  it  is  made.  The  second  pat  is  placed  in  the 
same  steam-bath  as  soon  as  it  is  set  hard,  and  can 
bear  the  I -pound  wire.  The  third  pat  is  placed  in 
the  steam-bath  after  double  the  interval  has  elapsed 
that  it  took  the  pats  to  set  hard,  counting  from  the 
time  of  gauging.  The  fourth  pat  is  placed  in  the 
steam-bath  at  the  end  of  twenty-four  hours. 

"  The  first  four  pats  are  each  kept  in  the  steam- 
bath  three  hours,  then  immersed  in  water  of  a  tem- 
perature of  about  200°  Fahr.  for  twenty-one  hours 
each,  when  they  are  taken  out  and  examined.  To  pass 
this  test  perfectly,  all  four  pats,  after  being  twenty- 
one  hours  in  hot  water,  should  upon  examination  show 

*  Transactions,  American  Society  of  Civil  Engineers,  vol.  xxvn. 
p.  412. 


178  HYDRAULIC   CEMENT. 

no  swelling,  cracks,  nor  distortions,  and  should  adhere 
to  the  glass  plates.  The  latter  requirement,  while  it 
obtains  with  some  cements  nearly  free  from  uncom- 
bined  lime,  is  not  insisted  upon,  the  cracking,  swelling, 
and  distortion  of  the  pats  being  much  the  more  im- 
portant features  of  this  test. 

"  In  hot-water  tests,  where  the  cement  is  very 
objectionable  from  excess  of  free  lime,  improper  burn- 
ing, or  other  causes,  the  trouble  generally  shows  itself 
in  the  cracking  or  distortion  of  all  four  pats.  Where 
the  cement  is  not  so  bad  the  cracking  and  swelling 
take  place  in  the  first  three  pats  only,  and  when  the 
cement  is  still  less  objectionable  only  the  first  two 
pats  crack  or  swell.  The  cracking  or  swelling  of 
No.  I  pat  alone  can  generally  be  disregarded." 

"  In  every  case  of  failure  and  rejection  the  cement 
should  have  been  allowed  to  set  hard  in  a  normal 
temperature  before  subjecting  it  to  a  steam-bath." 

It  should  be  noted  that  the  effect  of  exposing  the 
cement  to  steam  before  setting  seems  to  differ  with 
different  material,  depending  perhaps  upon  the  rela- 
tive effects  the  heat  may  exercise  upon  the  rate  of 
setting  and  upon  the  action  of  the  expansives.  Where 
the  rapidity  of  setting  is  greatly  increased  by  the  heat, 
the  severity  of  the  test  may  be  augmented  by  placing 
in  the  steam  at  once;  but  where  the  rate  of  setting  is 
less  affected,  the  heat  may  cause  the  action  of  the 
expansives  to  take  place  before  the  set,  thus  lessening 
the  severity  of  the  test.  In  most  cases  the  result  of 
the  test  is  the  same  either  way,  but  it  seems  fairer  to 
permit  the  cement  to  set  before  submitting  it  to  the 
test. 


TESTS   FOR   SOUNDNESS.  179 

Mr.  Maclay,  however,  in  his  specifications  does  not 
accept  the  results  of  the  steam  and  hot-water  test  as 
conclusive  in  case  of  failure,  but  only  considers  it  as 
cause  for  suspicion  of  the  cement  failing  to  pass  it, 
and  adds  a  further  test  for  the  purpose  apparently  of 
giving  the  material  one  more  chance.  This  test  con- 
sists in  testing  the  strength  of  briquettes  conserved  in 
hot  water  and  comparing  them  with  those  kept  cold. 

"  These  briquettes  are  prepared  and  treated  as  fol- 
lows: When  making  the  briquettes  for  the  ordinary 
cold-water  tests,  four  additional  sets  of  five  each  of 
neat  cement,  and  four  additional  sets  of  mortar,  one 
part  cement  and  two  parts  sand,  are  prepared,  and 
allowed  to  set  twenty-one  hours  in  moist  air  of  about 
60°  Fahr.  They  are  placed  for  three  hours  in  a 
steam-bath  about  195°  Fahr.,  then  immersed  in  water 
maintained  at  200°  Fahr.,  after  which  they  are  broken 
when  two,  three,  four,  and  seven  days  old  respec- 
tively, and  the  breakings  compared  with  the  normal 
breakings  of  briquettes  seven  and  twenty-eight  days 
old  kept  in  cold  water." 

"  The  writer  finds,  in  a  general  way,  that  the  aver- 
ages of  the  breakings  of  hot-water  briquettes  of  pure 
cement,  four  days  old,  are  nearly  as  high  as  the  nor- 
mal seven-day  breakings  cold,  and  the  hot  water  seven- 
day  breakings  of  the  pure  cement  are  nearly  as  high 
as  the  normal  twenty-eight-day  breakings  cold,  where 
the  cement  is  of  good  quality.  Where  the  cement  is 
poor,  and  the  pats  show  cracking  and  distortion,  there 
is  generally  a  remarkable  falling  off  in  the  strength  of 
the  hot-water  briquettes  from  the  above  comparison. 


ISO  HYDRAULIC  CEMENT. 

and  one  system  can  therefore  be  used  as  a  check  on 
the  other." 

This  is  practically  the  same  test  mentioned  in  Art. 
54,  as  proposed  by  M.  Le  Chatelier.  Its  use  in  this 
manner  is  recommended  by  M.  Candlot: 

"  The  cements  which  contain  free  lime  show  less 
resistance  in  hot  water  than  in  cold.  The  cements  of 
good  quality  in  hot  water  show  resistances  equal  to 
or  greater  than  those  in  cold.  Cements  properly 
proportioned  and  homogeneous,  but  not  completely 
burned,  give,  in  this  test,  satisfactory  results." 

As  already  pointed  out,  however,  the  relative 
strengths  hot  and  cold  do  not  depend  altogether  upon 
the  presence  of  expansives,  and  it  is  questionable  if 
this  method  is  as  accurate  as  that  it  is  designed  to 
check.  Some  unsound  materials  certainly  give  high 
results  in  the  measurement  of  the  strength  of  briquettes 
conserved  hot,  while  there  seems  to  be  no  authentic 
instance  of  any  unsound  cement  being  accepted  on  the 
steam  and  hot-water  test,  although  good  cement  may 
perhaps  be  condemned. 

ART.  57.     BOILING  TEST. 

The  boiling  test,  which  is  very  similar  in  effect  to 
that  by  steam  and  hot  water,  was  first  suggested  by 
Prof.  Tetmajer  of  Zurich.  It  consists  in  placing  the 
mortar  to  be  tested  in  cold  water,  and  then  gradually 
raising  the  temperature  of  the  water  to  boiling.  Prof. 
Tetmajer's  method  is  to  place  the  pats  in  cold  water, 
immediately  after  gauging,  raise  the  temperature  to 
boiling  in  about  an  hour,  continue  boiling  for  three 


TESTS   FOR   SOUNDNESS.  l8l 

hours.,  and  then  examine  the  pats  for  checking  and 
softening. 

This  method  seems  rather  more  severe  in  its  effects 
upon  the  mortar  than  the  other  hot  tests,  although  in 
general  differing  but  little  from  the  steam  and  hot- 
water  test  when  a  boiling  temperature  is  employed  in 
that  test;  the  action,  however,  seems  to  be  more 
energetic,  and  less  time  is  required  to  arrive  at  the 
same  results. 

It  seems  desirable  in  using  the  boiling  test  to  permit 
the  cement  to  set  before  subjecting  it  to  the  lest,  as 
giving  a  more  reliable  indication  of  value.  The  results 
of  the  test  is  in  most  cases  practically  the  same 
whether  the  cement  has  previously  set  or  not.  When 
cement  is  subjected  to  the  boiling  test  before  setting 
takes  place  it  is  necessary  to  exercise  much  care  in 
the  manipulation  of  the  test  to  avoid  any  disturbance 
of  the  mortar  through  the  motion  of  the  water  when 
heated.  The  results  of  the  test  also  depend  somewhat 
upon  the  rate  of  setting  of  the  material,  and  upon  the 
influence  of  heat  upon  the  rate  of  setting.  With 
quick-setting  cements  this  action  is  unimportant,  but 
with  those  very  slow  the  heat  may  cause  the  action 
of  the  expansives  to  take  place  in  advance  of  the 
setting,  or  the  cement  may  remain  soft  until  late  in 
the  test,  and  appear  to  fail,  in  consequence  of  dis- 
turbance due  to  the  ebullition  of  the  water. 

Prof.  Tetmajer  recommends  for  this,  and  in  fact  for 
all  pat  tests,  that  the  cakes  shall  not  be  made  with 
thin  edges.  His  method  is  to  roll  a  ball  of  the  mor- 
tar, and  then  flatten  the  ball  to  the  required  thickness. 
The  consistency  of  the  mortar  is  determined  by  the 


182  HYDRAULIC   CEMENT. 

requirement  that  it  shall  not  crack  in  flattening  or  run 
at  the  edges.  For  tests  in  boiling  water  this  seems 
desirable,  but  for  pats  to  be  used  in  the  ordinary  cold 
tests  the  thin  edges  are  of  advantage  in  expediting 
the  results  where  unsoundness  exists  in  the  mortar. 

The  boiling  test  is  frequently  used  in  connection 
with  apparatus  for  measuring  expansion,  in  place  of 
observing  the  distortions  or  cracks.  The  Bauschinger 
caliper  apparatus  is  sometimes  employed  in  this  way, 
the  bars  being  subjected  to  the  boiling  test,  and  the 
increase  in  length  noted.  The  Le  Chatelier  apparatus 
(Fig.  27)  is  also  usually  employed  in  this  manner. 
The  French  commission  upon  methods  of  testing 
materials  recommend  the  use  of  the  Le  Chatelier 
apparatus  for  this  purpose,  in  addition  to  the  cold  test 
given  in  Art.  52,  as  follows: 

"  Hot  Tests. — For  these  tests  cylindrical  test-pieces 
are  employed,  3  centimeters  in  diameter  and  3  centi- 
meters high,  made  in  metal  moulds  1/2  millimeter 
thick,  cut  on  a  generatrix,  and  carrying,  one  on  each 
side  of  the  slit,  two  needles,  1 5  centimeters  long.  The 
increase  of  the  distance  between  the  ends  of  the 
needles  gives  a  measure  of  the  swelling. 

"  The  molds  as  soon  as  they  are  filled  are  im- 
mersed in  cold  water.  After  an  interval  of  not  more 
than  twenty-four  hours  beyond  the  completion  of  the 
set  the  temperature  of  the  water  is  gradually  raised 
to  100°  C.  in  from  a  quarter  to  half  an  hour.  The 
temperature  is  maintained  at  100°  for  six  hours,  and 
then  it  is  allowed  to  cool  before  taking  the  final 
measurements." 


TESTS   FOR  SOUNDNESS.  183 

"  This  method  of  testing  is  not  applicable  to  quick- 
setting  cements." 

"  The  standard  test  for  deformation  is  to  be  made 
upon  neat  cement  of  standard  consistency." 

The  boiling  test  is  more  simple  than  the  steam  and 
hot-water  test,  and  requires  very  little  in  the  way  of 
apparatus.  It  may  readily  be  made  anywhere  without 
difficulty.  In  a  laboratory  where  apparatus  may  be 
kept  in  continuous  operation  the  steam  and  hot- 
water  test  offers  some  advantages  in  ease  of  operation, 
and  in  permitting  continuous  study  of  material  under 
examination  beyond  the  limits  of  the  regular  test. 

ART.  58.     PRESSURE  TEST. 

Dr.  Erdmenger  has  devised  a  high-pressure  steam 
test  for  soundness.  In  this  test  the  pats  are  allowed 
to  harden  for  three  days,  &nd  are  then  exposed  to 
steam  for  six  hours  at  a  pressure  of  from  3  to  20 
atmospheres.  The  originator  has  used  this  test  for  a 
number  of  years,  and  claims  that  it  gives  very  satis- 
factory results,  and  that  when  properly  carried  out  it 
enables  a  complete  and  rapid  judgment  to  be  formed 
on  a  cement  containing  magnesia.* 

As  with  all  accelerated  tests,  there  has  been  much 
dispute  as  to  the  reliability  of  this  one,  some  authori- 
ties claiming  that  many  of  the  best  Portland  cements 
fail  under  it,  others  considering  it  nearly  infallible. 
It  is  a  test  requiring  more  extensive  appliances  for  its 
execution  than  the  other  hot  tests,  and  has  not  been 
so  largely  used  as  the  others. 

*  Journal  Society  of  Chemkal  Industry,  vol.  XII.  p.  927. 


184  HYDRAULIC   CEMENT. 

The  test  is  executed  both  upon  the  neat  cement 
and  sand-mortar,  the  severity  of  the  test  being  greater 
upon  the  neat  cements.  Dr.  Erdmenger  claims  that 
the  best  cements  show  no  defect  under  this  test  at 
high  pressures  (forty  atmospheres);  that  others  may 
show  defects  at  high  pressures,  although  safe  in  prac- 
tice (especially  in  the  neat  test),  but  they  are  not  first 
quality;  while  cement  which  cannot  stand  the  pressure 
test  of  about  twelve  atmospheres  in  the  sand  tests 
should  be  rejected  as  faulty. 

ART.  59.     CHLORIDE-OF-CALCIUM  TEST. 

The  action  of  chloride  of  calcium  in  the  water  used 
in  gauging  or  conserving  the  briquettes  is  similar  to 
that  of  heat.  The  results  of  the  experiments  of 
M.  Candlot  have  already  been  discussed  (Art.  22). 
In  presence  of  calcium  chloride  the  slaking  of  lime  is 
greatly  accelerated,  the  effect  increasing  as  the  solu- 
tion is  more  concentrated.  It  also  makes  the  setting 
slower,  especially  for  cement  rich  in  aluminate  of  lime. 

If  cement  containing  free  lime  be  gauged  with  a 
concentrated  solution  of  calcium  chloride,  it  may 
therefore  cause  the  lime  to  become  slaked  before 
setting,  so  that  no  subsequent  swelling  will  take  place. 

If  the  solution  be  less  concentrated,  the  lime  may 
not  be  completely  slaked  before  setting  unless  the 
quantity  be  very  small,  while  the  slaking  is  hastened 
and  swelling  occurs  after  the  setting  if  the  free  lime 
be  in  sufficient  quantity. 

If  a  chloride-of-calcium  solution  is  used  to  keep  the 
cement  after  setting,  the  expansive  action  of  the  free 


TESTS  FOR  SOUNDNESS.  I»5 

lime  is  accelerated,  and  a  very  small  quantity  may 
produce  swelling. 

This  test,  as  devised  by  M.  Candlot,  is  to  mix  the 
cement  paste  with  a  feeble  solution  of  calcium  chloride, 
which  causes  the  slaking  before  setting  of  so  small  a 
percentage  of  lime  as  may  not  be  objectionable  in  the 
cement,  but  does  not  eliminate  a  larger  quantity. 
Then  immerse  the  mortar  in  the  same  solution,  and 
thus  augment  the  swelling  if  the  free  lime  be  present 
in  serious  quantity. 

The  method  of  conducting  the  test  as  proposed  is 
to  "  mix  the  paste  for  the  cakes  with  a  solution  of  40 
grammes  of  chloride  of  calcium  per  liter  of  water,  allow 
them  to  set,  immerse  in  the  same  solution  for  twenty- 
four  hours;  then  examine  for  checking  and  softening 
as  in  the  other  tests." 

The  chloride  of  calcium  is  said  to  exert  no  action 
upon  free  magnesia.  Upon  free  lime  it  seems,  how- 
ever, to  be  quite  efficient,  and  it  may  often  be  useful 
in  pointing  out  doubtful  material. 

The  action  becomes  less  energetic  as  the  tempera- 
ture is  increased,  and  it  should  not  be  used  in  con- 
nection with  the  hot  tests. 


ART.  60.     VALUE  OF  THE  ACCELERATED  TESTS. 

The  reliability  of  the  various  accelerated  tests  for 
determining  the  soundness  of  cement  in  use  is  a  matter 
concerning  which  there  is  much  dispute  amongst 
authorities  on  the  subject.  These  tests  have  not  as 
yet  come  into  general  use,  and  considerable  opposi- 


1 86  HYDRAULIC   CEMENT. 

tion  has  been  developed  to  them,  although  in  certain 
instances  they  are  employed. 

The  question  of  adopting  the  accelerated  tests  was 
discussed  by  the  Association  of  German  Cement 
Manufacturers  in  1891,  and  it  was  voted  to  adhere  to 
the  standard  test  already  existing.  It  was  also  stated 
in  the  report  that  experiment  had  not  proved  the  in- 
accuracy of  the  standard  test  (the  twenty-eight-day 
cold-pat  test),  and  while  the  accelerated  tests  may  be 
useful  to  the  manufacturers  in  determining  the  char- 
acter of  their  cements,  they  should  not  be  used  by  the 
consumer,  with  a  view  to  forming  a  sound  opinion  on 
the  constancy  of  volume. 

The  results  of  a  number  of  experiments  are  also 
given  in  this  discussion,  showing  that  a  number  of 
cements  which  had  not  withstood  the  kiln  test  were 
sound  when  used  under  water  at  normal  temperatures, 
or  if  placed  in  air  after  being  kept  moist  for  several 
days.  It  may  be  remarked  also  that  most  of  the  dis- 
cussion seemed  to  refer  mainly  to  the  dry-heat  test. 

Some  of  the  leading  German  cement  experts,  how- 
ever, are  strong  advocates  of  the  use  of  heat  tests. 
Dr.  Michaelis  expressed  his  approval  of  them,  and 
stated  that  he  had  experimented  with  and  used  them 
satisfactorily  for  a  number  of  years  at  the  Charlotten- 
burg  experiment  station.  Dr.  Erdmenger  also  declares 
that  experience  has  shown  the  high-pressure  steam 
test  to  give  an  accurate  determination  of  the  per- 
manence of  volume  of  the  material.  He  states  that 
most  of  the  best  German  cements  have  stood  this  test 
up  to  a  pressure  of  forty  atmospheres  for  sand-mortars 
and  several  for  neat  cement,  the  best  of  them  show- 


TESTS  FOR  SOUNDNESS.  l8/ 

ing  no  defect  whatever;  and  he  thinks  there  is  no 
ground  for  the  statement  that  many  good  cements 
will  not  pass  the  test. 

Prof.  Bauschinger  found  that  cements  which  had 
given  good  results  in  the  ordinary  28-day  test,  and 
also  upon  the  cold-pat  test  for  a  year,  failed  when 
formed  into  prisms  of  I  to  3  mortar  for  testing  in  the 
Bauschinger  caliper  apparatus.  Expansion  was  de- 
tected in  six  months  by  measurement,  and  afterward 
became  visible  to  the  naked  eye. 

The  German  Conference  upon  Methods  of  Testing* 
recommend  the  continuance  of  the  present  practice 
(the  kiln  test  for  quick  determinations  and  the  28-day 
cold-pat  test  as  decisive),  but  they  state  that  "  the 
boiling  test  may  undoubtedly  be  considered  as  the 
most  conclusive  and  rapid  test  for  the  determination 
of  constancy  of  volume  of  Portland  cement,  of  slag- 
cement,  and  of  trass,"  and  refer  a  particular  test  to 
the  sub-committee  for  further  examination  and  report. 

The  French  Commission  upon  Methods  of  Testing  f 
recommend  the  use  of  the  boiling  test  as  the  best 
method  of  arriving  at  a  quick  determination  of  the. 
permanence  of  volume  for  Portland  cement,  the 
amount  of  the  increase  in  volume  to  be  measured 
directly,  instead  of  simply  observing  the  effect  upon 
a  small  pat. 


*  Resolutions  of  the  Conventions  held  at  Munich,  Dresden, 
Berlin,  and  Vienna,  for  the  purpose  of  adopting  uniform  methods 
for  testing  materials,  by  J.  Bauschinger;  translated  by  O.  M. 
Carter  and  E.  A.  Gieseler  (Washington,  1896). 

f  Commission  des  Methodes  d'Essai  des  Materiaux  de  Construc- 
tion; Rapport  (Paris,  1894  and  1895). 


188  HYDRAULIC  CEMENT. 

In  England  the  steam  and  hot-water  test  has  been 
introduced  by  Mr.  Faija,  using  a  low  temperature; 
while  in  the  United  States  the  same  test  is  employed 
in  the  specifications  of  the  New  York  Department  of 
Docks,  using  temperature  near  boiling.  In  some  in- 
stances the  boiling  test  has  also  been  used  in  the 
United  States  by  manufacturers  in  the  study  of  their 
product,  with  very  good  results. 

The  advisability  of  adopting  some  form  of  acceler- 
ated test  in  ordinary  specifications  is  still  an  open 
question,  needing  for  its  determination  more  accurate 
knowledge  than  is  now  available  of  the  behavior  of  the 
various  kinds  of  cement  when  subjected  to  such  tests. 

Numerous  experiments  have  been  made  for  the 
purpose  of  deciding  the  matter,  the  results  of  which 
differ  so  widely  from  each  other  as  to  involve  the 
question  in  great  confusion.  Most  of  these  experi- 
ments have  been  made  by  studying  the  action  of  heat 
upon  the  various  ingredients  to  which  unsoundness 
is  usually  attributed,  and  arguing  from  the  results 
whether  the  hot  test  gives  an  accurate  indication  of 
the  presence  of  these  ingredients  in  the  cement.  The 
most  common  method  has  been  to  mix  a  small  quan- 
tity of  quicklime  with  a  good  Portland  cement,  and 
then  observe  the  action  of  the  test  upon  the  mixture. 
This  involves  the  assumption  that  certain  percentages 
of  free  lime  are  sufficient  to  render  the  cement  un- 
sound. The  results  of  tests  made  in  this  manner  are 
also  subject  to  much  variation,  due  to  the  nature  of 
the  cement,  its  rapidity  of  action,  and  the  quantity  of 
free  lime  which  may  have  been  originally  present  in 
it. 


TESTS  FOR  SOUNDNESS.  189 

These  experiments  have  been  of  much  value  in 
showing  the  effect  of  the  accelerated  tests  upon 
various  substances,  and  in  discovering  the  reasons  for 
many  of  the  apparently  contradictory  results  with 
them.  The  question  of  the  ultimate  adoption  of  tests 
of  this  character  must,  however,  be  determined  by  a 
comparison  of  the  results  obtained  by  their  use  upon 
the  material  as  found  in  market  with  the  action  of  the 
same  material  in  practical  use.  To  this  end  experi- 
ments are  desirable  which  shall  systematically  compare 
the  results  of  accelerated  tests  upon  ordinary  cements 
with  the  results  of  tests  under  normal  conditions  ex- 
tended over  long  periods  of  time.  An  extended  series 
of  experiments  of  this  character  has  already  been  car- 
ried out  by  Prof.  Tetmajer  at  Zurich,*  and  a  smaller 
series  upon  material  in  use  in  the  United  States  at 
the  laboratory  of  the  College  of  Civil  Engineering  at 
Cornell  University. 

A  careful  study  of  the  available  results  of  experi- 
ment seems  to  justify  the  following  statements: 

1.  Small  percentages  of  uncombined  lime  or  mag- 
nesia in  the  cement  are  commonly  detected  by  the  use 
of  the  heat  tests,  and  the  same  ingredients  in  suffi- 
cient quantity  render  the  cement  unsound  in  ordinary 
use. 

2.  Cement  liable  to  change  of  volume  when  em- 
ployed under  normal  conditions  is  almost  invariably 
detected    when    submitted    to    the    hot-water    test. 
There  seems  to  be  no  well-authenticated  instance  of 
failure  to  condemn  really  defective  material. 

*  Methoden  und  Resultate  der  Priifung  hydraulischen  Binde- 
mittel  (Zurich,  1893). 


190  HYDRAULIC  CEMENT. 

3.  Nearly,  if  not  quite,  all  of  the  best  brands  of 
Portland   cement,    and   many  of    natural  cement,   as 
found  in   market,   readily  meet  the  requirements  of 
these  tests,  which  therefore  do  not  impose  so  severe 
limitations  upon  the  choice  of  cement  as  is  commonly 
supposed.     With  natural  cement  the  results  of  these 
tests  vary  somewhat  with  the  character  of  the  cement, 
and  the   same  tests  do    not  seem  to  be    universally 
applicable.      This,   however,    is  a   matter  which   can 
only  be  determined  by  careful  experiment  upon  each 
of  the  various  classes  of  natural  cement.      Many  of 
them  bear  the  severe  tests  fully  as  well  as  the  Port- 
land. 

4.  While  these  tests  rarely,  if  ever,  fail  to  detect  an 
unsound  cement,  and  most  good  cements  readily  pass 
them,  there  are  occasional  instances  of  cements  con- 
demned  by  the  heat   tests,   which  are   not   unsound 
when   kept   at  normal  temperatures  in    fresh  water. 
These  cements  for  the  most  part  seem  to  fail  if  kept 
in  dry  air  or  are  subjected  to  the  action  of  sea-water. 
Apparently,  a  degree  of  unsoundness  may  exist  which 
is  sufficient  to  cause  the  change  of  volume  to  take 
place  in  a  short  time  in  hot  water  or  in  a  longer  time 
in  dry  air,  while  in  cold  water  the  action  of  the  ex- 
pansives  takes  place  without  injury   to  the    mortar. 
This  is  shown  by  the  fact  that  pats  of  mortar  which 
had  failed  in  the  boiling  test   at  the  time  of  mixing, 
after  being  kept  several   months  in  cold  water,  and 
then    subjected    to    the  boiling  test,  were  found  to 
stand  the  test  perfectly,  showing  that  the  action  of 
the  expansives  must  meanwhile  have  taken  place.      In 


TESTS  FOR   SOUNDNESS.  IQI 

several  instances  pats  of  cement  acting  in  this  manner 
were  found  to  blow  in  dry  air. 

The  unsoundness  of  cement  condemned  by  the  heat 
tests,  when  the  mortar  is  to  be  kept  submerged  in 
fresh  water,  is  therefore,  in  many  instances  at  least, 
questionable.  In  the  large  series  of  tests  made  by 
Prof.  Tetmajer,  out  of  139  samples  of  Portland 
cement  17  failed  in  the  boiling  test,  all  of  which  also 
failed  in  a  long  time  in  dry  air,  while  only  2  were 
defective  in  long  time  in  fresh  cold  water.  In  the 
tests  made  by  the  author,  the  percentage  of  failures  to 
total  number  of  samples  is  less  than  at  Zurich,  5  in 
53,  and  3  of  the  5  samples  which  were  rejected  by  the 
hot  test  were  later  disintegrated  when  kept  in  cold 
fresh  water. 

5.  The   fineness  of  the  cement  has  an  important 
bearing  upon  its  behavior  under  the  heat  tests.     All 
ordinary  cement  probably  contains  some  small  propor- 
tion of  expansives,  which  in  the  finely  ground  material 
may  become  hydrated  without  injury  to  the  mortar; 
but  if  the  fine  material  be  sifted  out,  and  only  the 
coarse  particles  employed  in  the  test,  the  slower  action 
in  the  larger  particles  may  cause  distortion  and  crack- 
ing   to    take    place.     Whether   the    same    difference 
usually  follows  in  cold  water  has  not  been  satisfactorily 
determined. 

6.  Portland   cement  which   contains    free    lime    in 
sufficient  quantity  to  cause  it  to  swell  in  the  hot  test 
may  frequently  be  made  to  pass  that  test  by  adding 
a  small  quantity  of  sulphate  of  lime.     The  action  of 
this  salt  upon  the  setting  of  cement  has  already  been 
discussed  (Art.  21).     The  rules  of  the  Association  of 


IQ2  HYDRAULIC   CEMENT. 

German  Cement  Makers  permit  the  addition  of  a  small 
proportion  of  sulphate  of  lime  for  the  purpose  of 
regulating  the  rate  of  setting,  and  conclude  that  no 
injury  is  thereby  caused  to  the  cement. 

The  action  of  the  sulphate  of  lime  to  correct  the 
expansive  action  of  free  lime  is  but  imperfectly 
known.  The  fact  that  it  causes  cement  containing 
free  lime  to  pass  the  hot  tests  is  well  known,  but 
whether  the  corrective  influence  extends  to  the  action 
of  the  expansives  when  the  material  is  used  under 
normal  conditions  has  not  as  yet  been  satisfactorily 
determined. 

The  strongest  objection  that  has  been  urged  against 
the  use  of  hot  tests  is  that  they  fail  to  detect  free 
lime  in  the  presence  of  the  calcium  sulphate.  The 
justice  of  this  objection  can  only  be  decided  by  ex- 
periments extending  over  considerable  periods  of  time 
to  determine  whether  the  material  so  passed  is  sound 
under  normal  conditions.  Doubtless  for  use  in  sea- 
water  it  would  be  necessary  to  limit  the  quantity  of 
sulphuric  acid. 

The  whole  subject  of  hot  tests  must  still  be  regarded 
as  in  the  experimental  stage,  and  further  experiment 
is  necessary  to  determine  more  fully  the  connection 
between  the  results  of  tests  and  the  action  of  the 
cement  in  use. 

Under  present  conditions  it  may  be  said  that  the 
presumption  is  fairly  against  the  soundness  of  a 
cement  failing  to  pass  the  hot-water  test  and  in  favor 
of  that  which  succeeds  in  passing  it;  but  variations  in 
the  cement  and  in  the  conditions  under  which  it  is 
employed  may  affect  the  results,  and  they  cannot  be 


TESTS  FOR  SOUNDNESS.  193 

relied  upon  with  certainty  for  all  material.  Upon 
ordinary  work  to  be  kept  in  fresh  water  there  is 
probably  no  considerable  danger  of  unsoundness  in  the 
use  of  any  good  brand  of  cement,  although  failure 
sometimes  occurs;  but  for  the  more  important  works, 
and  particularly  those  to  be  subjected  to  the  action 
of  sea-water,  it  is  reasonable  to  apply  such  tests  as  are 
likely  to  insure  good  material,  even  at  the  risk  of  ex- 
cluding other  good  material. 

ART.  61.    AIR-SLAKING. 

Sometimes  fresh  cement,  when  first  opened  after 
being  shipped,  will,  if  tested  at  once,  show  an  abnor- 
mally rapid  rate  of  setting,  and  subsequently  harden 
very  slowly,  so  that  on  short-time  tests  very  low  ten- 
sile strength  may  be  given.  If,  however,  this  cement 
be  exposed  to  the  air  for  a  few  days,  it  may  resume 
its  natural  rate  of  setting,  and  attain  proper  strength 
upon  the  tests.  In  some  laboratories  it  is  customary 
to  thus  expose  cement  to  the  air  a  short  time  before 
testing,  and  this  process  is  termed  air-slaking. 

The  propriety  of  air-slaking  in  testing  cement  is 
questioned  by  some  engineers,  upon  the  ground  that 
the  cement  to  be  used  in  the  work  will  not  be  treated 
in  the  same  manner.  In  England  it  is  customary  to 
give  such  exposure  to  all  cement  to  be  used  upon  im- 
portant work  for  at  least  ten  days,  but  in  the  United 
States  the  cement  is  commonly  used  just  as  received 
from  the  manufacturer. 

The  general  practice  seems  to  favor  air-slaking  in 
testing,  and  probably  a  cement  capable  of  regaining 


194  HYDRAULIC  CEMENT. 

its  normal  condition  in  a  few  days'  exposure  will  not 
endanger  the  work,  even  if  used  at  once,  but  it  would 
doubtless  be  better  in  using  such  cement  to  air-slake 
the  whole  before  using.  It  may  be  remarked,  how- 
ever, that  air-slaking  does  not  ordinarily  seem  neces- 
sary. The  cement  commonly  placed  upon  the  market 
by  the  best  makers  does  not  need  it.  While  it  may 
be  allowable  to  give  the  material  the  benefit  of  the 
operation,  probably  few  instances  of  rejection  would 
occur  on  account  of  its  omission. 

In  many  instances  the  effect  of  air-slaking  a  cement 
requiring  it  disappears  with  time;  that  is,  the  strength 
of  the  mortar  after  three  or  six  months  may  be  as 
great  for  that  mixed  before  as  for  that  mixed  after  air- 
slaking,  although  the  difference  of  strength  on  a  test 
extending  over  a  few  days  is  very  considerable.  This 
would  indicate  the  necessity  of  air-slaking  the  whole 
of  the  material  if  early  strength  is  to  be  developed  in 
the  work,  although  the  ultimate  strength  might  per- 
haps be  satisfactory  either  way. 

If  the  cement  blows  or  shows  unsoundness  on  the 
first  test,  it  should  not  be  used  without  exposure,  as 
it  would  indicate  a  degree  of  unsoundness  likely  to  be 
serious,  even  though  this  also  disappear  in  the  second 
test. 

The  question  is  simply  as  to  the  quantity  of  the 
expansives  which  may  be  present  without  danger  to 
the  work  in  which  it  is  used. 


CHAPTER   VIII. 
SPECIAL  TESTS. 

ART.  62.     TESTS  OF  ADHESIVE  STRENGTH. 

THE  ability  of  cement-mortar  to  firmly  adhere  to 
any  surface  with  which  it  may  be  placed  in  contact  is 
one  of  its  most  valuable  properties,  and  quite  as  impor- 
tant as  the  development  of  cohesive  strength.  Tests 
for  adhesive  strength  are  not  commonly  employed 
as  a  measure  of  the  quality  of  the  material,  because  of 
the  uncertain  character  of  the  test  and  the  difficulty  of 
so  conducting  it  as  to  make  it  a  reliable  indication  of 
value.  The  adhesive  properties  of  the  cement  are  to 
a  certain  extent  called  into  play  in  the  tensile  tests 
of  sand-mortar,  and  may  be  inferred  from  a  compari- 
son of  neat  and  sand  tests. 

Adhesive  strength  is  developed  more  slowly  than 
that  of  cohesion.  The  difference  between  the  two, 
which  is  usually  considerable  during  the  early  period 
of  hardening,  is  gradually  lessened  with  time.  This 
is  illustrated  in  the  greater  time  required  for  sand- 
mortar  than  for  neat  cement  to  harden. 

Experiments  u-pon  the  adhesion  of  mortars  to 
various  substances  are  sometimes  made,  both  for  the 
purpose  of  comparing  various  cements  or  methods  of 
use,  and  to  study  the  relative  effects  of  various  kinds 

195 


196 


HYDRAULIC   CEMENT 


of  surfaces.  Such  experiments  are  quite  desirable 
with  a  view  to  the  extension  of  knowledge  of  this  very 
important  quality. 

The  common  method  of  making  this  test  is  to  pre- 
pare briquettes,  of  which  one  half  are  of  neat  cement 
or  sand-mortar  of  the  ordinary  form  for  tensile  speci- 
mens, and  the  other  half  a  block  of  stone,  glass,  or 
other  material  to  be  used,  of  the  same  section  as  the 
mold  at  its  middle,  and  arranged  to  be  held  by  a 
special  clip  in  the  testing-machine  at  the  other. 

In  Germany  and  Switzerland  the  apparatus  shown  in 
Fig.  28  is  employed.  The  test-piece  is  shown  at  a; 


FIG.  28. 

it  has  a  section  of  10  square  centimeters — twice  that 
of  the  standard  tensile  specimen.  The  mortar  end  is 
enlarged  to  a  wedge  shape  to  catch  the  upper  clip  of 
the  testing-machine,  while  the  other  end  is  formed  of 
a  parallelepiped  of  marble  or  ground  glass  for  standard 
tests,  with  a  cylindrical  groove  cut  in  its  side,  which 
fits  into  a  special  clamp  (shown  at  c].  This  clamp  is 
held  by  screws  in  the  lower  clip  of  the  testing-machine, 
as  shown  at  d.  For  forming  the  briquettes  molds 


SPECIAL  TESTS.  197 

are  used,  in  the  bottom  of  which  the  blocks  are  placed 
and  the  mortar  filled  in  on  top. 

In  some  laboratories  blocks  of  marble  have  been 
used  for  standard  tests  in  comparing  different  ma- 
terials; but  the  large  amount  of  labor  involved  in  the 
preparation  of  the  blocks,  and  the  difficulty  of  getting 
always  the  same  surface,  has  been  a  bar  to  the  exten- 
sion of  this  method.  Ground  glass  has  been  more 
commonly  employed,  the  same  blocks  being  repeatedly 
used.  Dr.  Michaelis  has  also  used  for  this  purpose 
standard  blocks  of  cement-mortar,  of  the  same  form, 
which  are  easily  prepared,  and  more  uniform  in 
material  and  surface. 

The  German  Conference  on  Methods  of  Testing, 
before  mentioned,  did  not  define  a  standard  test,  but 
referred  the  matter  to  a  sub-committee,  with  the 
recommendation  that  the  German  apparatus  just 
described  be  utilized. 

The  French  commission  recommend  the  use  of  a 
briquette  of  double  T  form,  suggested  by  M.  Candlot. 
It  is  shown  in  Fig.  29.  A  mold  is  employed,  made 
to  the  form  of  half  the  briquette,  which  is  set  down 
over  the  block  to  be  used  in  forming  the  specimen. 

The  recommendations  of  the  commission  are  as 
follows : 

"  A.  To  compare  the  adhesive  strengths  of  cements, 
there  is  submitted  to  the  tension  test  a  briquette  of 
the  double  T  form,  shown  above,  each  of  the  ma- 
terials to  be  studied  constituting  half  of  one  of  the 
specimens. 

"  B.   Standard  tests,  intended  to  compare  the  ad- 


I98 


HYDRAULIC   CEMENT. 


hesive  strengths  of  various  cements  to  the  same  ma- 
terial. 

"  (a)  The  standard  adhesion-blocks  are  prepared  of 
mortar  composed  of  one  part,  by  weight,  of  artificial 
Portland  cement,  passed  thiough  the  sieve  of  900 
meshes  per  square  centimeter,  and  two  parts  of  stand- 
ard sand  No.  3  (that  passing  a  sieve  of  i  mm.  open- 


FIG.  29. 

ings  and  retained  upon  one  of  1/2  mm.  openings). 
The  mortar  is  gauged  with  9  per  cent  water  and 
strongly  compressed  in  the  moulds,  in  the  bottom  of 
which  is  placed  a  movable  metallic  block.  The  ad- 
hesion-blocks are  immersed  in  fresh  water  after 
twenty-four  hours,  and  kept  thus  until  used,  or  at 
least  for  twenty-eight  days.  When  they  are  to  be 
utilized,  they  are  dried  and  the  surface  is  smoothed 
with  emery  paper. 

"  (b)  The  standard  plastic  mortar  (see  Art.  44)  is 
employed  for  these  tests,  introduced  by  the  pressure 


SPECIAL   TESTS.  199 

of  the  trowel  into  the  moulds,  placed  in  such  manner 
that  the  standard  adhesion-block  forms  the  base. 
The  briquette  is  removed  from  the  mould  when  com- 
pletely set." 

"  (c)  The  briquettes  are  tested  in  the  same  manner 
and  at  the  same  periods  prescribed  for  tensile  tests." 

"  C.  Tests  intended  to  compare  the  adhesive 
strength  of  a  cement  to  various  materials; 

' '  (a)  For  these  tests  the  same  methods  are  adopted, 
with  the  difference  that  the  standard  blocks  are  re- 
placed by  blocks  formed  of  the  various  materials  to  be 
used.  If  the  material  can  be  moulded  the  block  may 
be  made  in  the  same  way  as  the  standard  block.  If 
the  material  is  solid,  a  plate  several  millimeters  thick 
may  be  formed  having  one  face  dressed.  This  is 
placed  in  the  bottom  of  the  mould  and  the  block  filled 
out  with  neat  cement." 

ART.  63.     CHEMICAL  ANALYSIS. 

Chemical  analysis  is  of  very  great  value  in  the  study 
of  the  properties  of  various  cements,  and  is  com- 
monly employed  by  manufacturers  in  regulating  the 
quality  of  their  products.  It  is  not  commonly  used 
for  the  purpose  of  determining  the  quality  of  a  cement, 
and  is  not  of  much  value  as  a  test  for  the  reception  of 
material. 

The  quality  of  the  cement  depends  not  only  upon 
the  ingredients  being  properly  proportioned,  but  also 
upon  the  state  of  combination  of  the  ingredients,  and 
this  in  turn  depends  upon  the  manipulation  given  the 
material  in  manufacture.  Analysis  shows  the  propor- 


2OO  HYDRAULIC   CEMENT. 

tions  of  the  various  ingredients,  but  does  not  show 
their  state  of  combination.  The  results  of  an  analysis 
may  show  that  the  composition  is  such  that  a  good 
cement  may  be  made  from  the  ingredients,  but  other 
tests  are  necessary  to  show  whether  it  has  been  made. 
Chemical  analysis  .may,  however,  prove  a  cement  to 
be  bad  through  its  containing  objectionable  propor- 
tions of  ingredients  known  to  be  injurious.  Thus  the 
allowable  percentage  of  sulphur  compounds  is  some- 
times prescribed  for  cement  to  be  used  in  maritime 
work;  in  fresh  water  they  may  be  unobjectionable. 
The  expansive  elements,  free  lime  or  free  magnesia, 
cannot  be  detected  by  analysis,  as  their  presence  is 
not  necessarily  dependent  upon  the  proportions  of 
total  lime  or  magnesia  present. 

The  French  specifications,  devised  by  M.  Guillain, 
for  Portland  cement  reject  those  containing  more  than 
1$  of  sulphuric  acid,  or  sulphides  in  appreciable  quan- 
tity; while  those  containing  more  than  4$  of  oxide  of 
iron,  or  which  give  less  than  44/100  for  the  ratio  of 
the  sum  of  the  weights  of  silica  and  alumina  to  the 
weight  of  the  lime  are  to  be  regarded  with  suspicion. 

A  large  percentage  of  volatile  elements  in  a  cement 
indicate  -either  insufficient  burning  or  deterioration 
with  age  through  exposure  to  the  air. 

M.  Candlot  states  that  a  chemical  analysis  may  be 
useful  in  showing  the  adulteration  of  cement,  some- 
times practised  in  Europe.  Upon  sifting  the  cement 
and  separately  analyzing  the  coarse  and  fine  portions 
an  unadulterated  cement  should  show  practically 
identical  results  for  the  two  analyses.  He  also  states 
that  blast-furnace  slag,  which  is  a  common  adultera- 


SPECIAL  TESTS.  2OI 

tion  in  Portland  cement,  may  sometimes  be  discovered 
by  the  odor  of  sulphuretted  hydrogen  upon  treating 
it  with  hydrochloric  acid. 

Method  of  Analysis. — The  following  method  of 
making  an  analysis  of  cement  is  given  by  M.  Durand- 
Claye:* 

"  Weigh  two  grammes  of  the  specimen  in  powder, 
place  in  a  porcelain  evaporating-dish  with  a  little 
water  and  hydrochloric  acid  in  excess.  Evaporate 
dry  in  a  sand-bath  at  a  moderate  temperature.  The 
mass  should  be  stirred  several  times  with  a  glass  rod 
after  the  silica  has  jellied.  When  the  drying  is  com- 
plete, place  the  dish  in  a  furnace  and  heat  quickly, 
but  not  to  redness,  to  remove  the  last  trace  of  acid  and 
humidity.  After  cooling,  treat  the  new  material  with 
a  slight  excess  of  hydrochloric  acid,  and  evaporate 
a  second  time  to  dryness.  Then  treat  again  with 
acidulated  water.  The  liquor  should  appear  yellow, 
and  the  residue  white,  not  reddish.  If  it  has  that 
color,  let  the  dish  and  its  contents  heat  some  time  in 
a  sand-bath  until  all  the  red  color  disappears. 

"  Silica. — Place  the  contents  of  the  dish  upon  a  fil- 
ter. The  white  powder  obtained  is  the  silica  of  the 
specimen.  Dry,  calcine,  and  weigh  in  the  ordinary 
manner. 

"Silicious  Sand. — The  cement  sometimes  contains 
grains  of  inert  silicious  sand,  which  is  found  with  the 
silica.  It  is  recognized  by  the  sound  of  the  grains  on 
the  bottom  of  the  dish  when  stirred  with  the  glass  rod. 
To  determine  the  silicious  sand,  dissolve  the  cement 

*  Chimie  appliquee  a  1'art  de  1'ingenieur  (Paris,  1885). 


2O2  HYDRAULIC   CEMENT. 

in  hydrochloric  acid,  and  let  the  liquor  digest  during 
one  day.  Then,  upon  decanting,  the  silicious  grains 
rest  upon  the  bottom;  wash,  collect,  and  weigh. 

"Alumina  and  Iron. — The  filtrate,  after  removing 
the  silica,  is  treated  with  a  few  drops  of  nitric  acid, 
and  brought  to  ebullition  for  a  moment.  The  pro- 
toxide of  iron,  if  any,  is  transformed  to  peroxide. 
Then,  by  saturating  with  a  slight  excess  of  ammonia, 
and  boiling,  a  precipitate  is  formed,  which  is  collected 
on  a  filter  placed  in  a  funnel  above  a  flask.  It  is 
washed  carefully  with  warm  water.  When  well  drained, 
it  is  placed  on  a  sand-bath,  dried,  burned,  and  weighed. 
The  weight  found,  diminished  by  that  of  the  cinders 
of  the  filter,  is  that  of  the  peroxide  of  iron  and 
alumina  soluble  in  acids.  The  ammonia  precipitates 
the  two  bases  from  the  solution,  while  it  is  without 
effect  upon  the  salts  of  lime,  and  does  not  affect  the 
salts  of  magnesia  previously  acidulated.  When  the 
limestone  contains  much  magnesia,  like  dolomite, 
some  of  that  base  may  be  precipitated  by  the  ammonia. 
In  this  case  it  is  prudent  to  redissolve  the  precipitate 
in  hydrochloric  acid,  after  having  separated  by  filtra- 
tion, and  to  reproduce  it  a  second  time  with  ammonia. 

"  Lime. — Add  oxalate  of  ammonia  to  the  last  fil- 
trate, and  the  lime  only  is  precipitated,  as  magnesia  is 
not  separated  in  the  water  containing  ammonia  salts. 
In  order  that  the  oxalate  of  lime  may  be  well  precipi- 
tated, it  is  necessary  to  employ  a  large  excess  of  the 
reagent.  The  precipitate  is  collected  better  when  the 
temperature  is  higher;  it  is  therefore  well  to  heat  the 
liquor,  and  dissolve  the  oxalate  of  ammonia  in  boiling 
water.  In  order  to  obtain  a  complete  precipitation 


SPECIAL  TESTS.  2O3 

the  liquor  must  be  alkaline.  The  precipitate  should 
not  be  filtered  immediately,  as  the  liquor  continues 
working.  The  flask  should  be  put  in  a  furnace  and 
boiled  for  half  an  hour,  or  still  better  be  left  in  a 
sand-bath  half  a  day.  The  boiling  in  the  furnace 
of  a  grainy  precipitate  like  oxalate  of  lime  gives 
rise  frequently  to  shocks,  which  perhaps  throws  the 
material  out.  When  the  precipitate  is  well  formed 
and  the  liquor  clear,  place  upon  a  filter  in  a  funnel 
over  a  flask  and  wash  carefully  with  hot  water;  then, 
placing  the  funnel  in  a  sand-bath,  dry  the  filter  and 
precipitate  before  calcining.  A  simple  scorching  is 
not  sufficient.  The  oxalate  at  the  temperature  of 
burning  is  decomposed  more  or  less  completely:  a 
part  becomes  caustic  lime;  some  is  transformed  to 
carbonate,  or  it  remains  as  oxalate.  It  is  therefore 
necessary  to  transform  it  to  a  definite  compound. 

"  When  the  means  are  at  hand  for  a  sufficiently 
energetic  burning  to  heat  the  platinum  cherry-red, 
put  the  precipitate,  with  the  filter,  in  a  platinum 
crucible  furnished  with  a  cover,  and  calcine.  Five 
minutes  are  sufficient  with  an  annealing  bellows.  The 
oxalate  is  transformed  to  caustic  lime,  which  is  imme- 
diately weighed  in  the  crucible  when  cold.  •  The 
weight,  less  cinders  of  filter,  is  the  lime  contained  in 
the  sample.  It  is  well  to  assure  that  the  calcination 
is  complete;  for  this  purpose,  after  weighing,  pour  a 
little  water  in  the  crucible,  then  acid;  if  any  carbon- 
ate is  present,  bubbles  of  gas  will  be  given  off. 

"  When  an  apparatus  for  heating  so  energetically 
is  lacking,  the  oxalate  is  sometimes  changed  to  car- 
bonate. Place  the  precipitate  in  a  platinum  dish  and 


204  HYDRAULIC  CEMENT. 

burn  in  a  muffle,  or  to  a  heat  which  makes  the  dish 
red.  When  it  is  cold,  pour  a  solution  of  carbonate 
of  ammonia;  then  evaporate  in  a  sand-bath,  dry  over 
a  furnace,  and  weigh.  It  is  well  to  renew  the  treat- 
ment of  carbonate  of  ammonia  until  two  weights  are 
obtained  which  are  in  accord.  The  weight  of  lime  is 
0.56  that  of  the  carbonate. 

"  Magnesia. — The  filtrate  contains  the  magnesia, 
with  the  ammonia  salts  which  are  introduced  in  the 
course  of  the  analysis.  Precipitate  with  phosphate  of 
soda.  Let  it  stand  cold  half  a  day  before  filtering, 
until  finally  assured  that  the  ammonia-magnesian 
phosphate  which  is  formed  is  entirely  crystallized,  or 
at  least  that  not  more  than  insensible  traces  remain  in 
solution.  When  placed  on  the  filter  some  of  the 
crystals  adhere  to  the  flask,  and  may  not  be  detached 
by  washing.  These  are  dissolved  in  acid  and  then 
again  precipitated  with  ammonia  in  non-adherent 
granular  crystals,  which  readily  wash  upon  the  filter. 
The  washing  from  the  flask  to  the  filter  should  be 
done  with  cold  water  charged  with  ammonia.  Pure 
water,  especially  if  warm,  dissolves  an  appreciable 
quantity  of  the  precipitate.  After  drying,  burn  with 
the  filter  and  weigh.  40/111  of  the  weight,  less  the 
cinders  of  the  filter,  gives  the  weight  of  magnesia. 

"  Volatiles. — Weigh  a  new  specimen  in  a  crucible 
and  calcine  quickly  for  five  or  ten  minutes.  The 
crucible  when  cold  is  weighed  with  its  contents,  which 
are  composed  of  lime  and  the  other  fixed  elements. 
The  difference  in  weight  is  the  loss  upon  ignition. 

"  Sulphuric  Acid. — If  it  is  desired  only  to  obtain 
the  sulphate  of  lime,  take  a  specimen  (5  grammes  for 


SPECIAL  TESTS.  2O$ 

example)  and  digest  cold  in  a  solution  of  carbonate  of 
ammonia  for  twenty-four  hours.  Agitate  the  mix- 
ture often,  especially  in  the  beginning.  The  sulphate 
of  lime  is  decomposed,  carbonate  of  lime  and  sul- 
phate of  ammonia  being  produced.  Filter,  saturate 
the  liquor  with  hydrochloric  acid,  and  boil  to  remove 
all  carbonic  acid.  Then  pour  in  chloride  of  barium, 
and  the  sulphuric  acid  is  precipitated  as  sulphate  of 
barium,  which  is  collected  on  a  filter,  dried,  and 
weighed.  The  filtration  should  not  take  place  imme- 
diately: it  should  stand  until  the  sulphate  of  barium 
gathers  and  the  liquor  clears. 

"  Sulphides. — If  the  total  sulphur  is  to  be  obtained, 
it  is  to  be  brought  into  contact  with  an  oxidant,  which 
transforms  the  sulphide  into  sulphate.  A  little  chlo- 
rate of  potassium  is  added,  and  then  it  is  attacked  with 
precaution  by  hydrochloric  acid.  Evaporate  dry,  and 
digest  the  residue,  after  cooling,  with  carbonate  of 
ammonia.  The  analysis  is  then  like  the  preceding. 
If  the  two  methods  be  simultaneously  applied,  and  by 
the  second  a  result  be  found  larger  than  by  the  first, 
the  difference  represents  the  sulphuric  acid  formed 
from  the  sulphides. 

"  Alkali. — Take  a  special  specimen  and  separate 
the  silica,  alumina,  and  iron  as  already  indicated. 
Pour  the  filtrate  so  obtained  in  a  porcelain  dish  and 
evaporate  dry,  then  calcine  in  a  muffle  to  drive  off  the 
ammonia  salts  and  decompose  the  oxalates.  The 
residue  is  composed  of  alkaline  salts,  and  of  magnesia, 
free  or  carbonated.  The  latter  are  insoluble,  and  by 
treating  with  water  and  filtering,  a  liquor  is  obtained 
containing  only  the  alkaline  salts.  The  liquor  is 


2O6  HYDRAULIC   CEMENT. 

evaporated  to  dry  ness  in  a  platinum  dish  in  presence 
of  an  excess  of  sulphuric  acid,  which  displaces  the 
other  acids.  The  residue  is  alkaline  sulphate.  Heat 
to  redness  to  drive  off  all  excess  of  acid,  and  weigh. 
Treat  with  water  acidulated  with  hydrochloric  acid, 
and  precipitate  the  sulphuric  acid  with  chloride  oi 
barium.  The  weight  of  sulphate  of  barium  gives  that 
of  sulphuric  acid,  which  subtracted  from  that  of  the 
alkaline  sulphates  gives  fixed  alkali. 

"  When  the  specimen  contains  considerable  sul- 
phuric acid  this  method  may  give  erroneous  results. 
The  sulphate  of  magnesia  is  only  partially  decomposed 
at  the  moment  of  calcination  of  the  ammonia  salts, 
and  a  part  of  that  salt  is  found  with  the  alkaline  sul- 
phates. To  remove  that  cause  of  error,  after  having 
eliminated  the  ammonia  salts  and  treated  the  residue 
with  water,  pour  on  a  little  baryta  water,  which  pre- 
cipitates the  magnesia  and  gives  at  the  same  time 
compounds  insoluble  in  sulphuric  or  carbonic  acid. 
The  filtrate  contains  then  only  alkaline  chlorides,  free 
alkali,  and  baryta.  Saturate  with  sulphuric  acid  and 
filter,  then  evaporate  dry,  and  calcine,  and  obtain  the 
residue  of  alkaline  sulphates  as  in  the  other  case. 

"  Separation  of  Iron  and  Alumina. — After  having 
burned  and  weighed  these  two  bases,  digest  and  heat 
with  hydrochloric  acid  until  dissolved.  Mix  with 
citric  or  tartaric  acid  until  ammonia  in  excess  does 
not  produce  a  precipitate ;  then  add  the  sulphohydrate 
of  ammonia.  The  alumina  is  not  precipitated,  while 
the  iron  passes  to  the  state  of  insoluble  sulphide. 
Boil  and  collect  on  a  filter,  dry,  burn,  and  weigh. 
The  sulphide  decomposes  and  becomes  peroxide. 


SPECIAL  TESTS.  2O/ 

The  alumina  is  the  difference  between  the  total 
weight  and  that  of  the  peroxide  of  iron. 

"  Or,  after  dissolving  in  hydrochloric  acid,  evaporate 
the  larger  part  of  the  hydrochloric  liquid  so  as  to  have 
a  slight  excess  of  acid;  then  pour  a  solution  of  pure 
potash  in  excess,  and  boil  until  the  precipitate  obtained 
presents  a  dark  reddish  brown  color.  Filter  and 
wash  the  precipitate  of  peroxide  of  iron.  An  appre- 
ciable quantity  of  alumina  will  be  precipitated  with 
the  iron;  to  remove  this,  redissolve  in  hydrochloric 
acid  and  repeat  the  operation  a  second  or  third 
time.  The  absence  of  alumina  is  shown  by  the 
ammonia  salt  giving  no  precipitate  with  the  filtrate. 

"  This  operation  requires  great  care  and  consider- 
able time." 

ART.  G4.     TESTS  FOR  HOMOGENEITY. 

In  Europe  various  tests  have  been  proposed  for  the 
purpose  of  detecting  the  adulteration  of  Portland 
cement.  These  tests  are  not  usually  of  a  nature  in- 
tended for  use  in  specifications  for  the  reception  of 
material,  but  may  sometimes  be  of  use  in  studying  the 
characteristics  of  various  brands  of  cement  or  in  classi- 
fying a  product  of  doubtful  character.  The  materials 
sometimes  met  with  as  adulterations  include  powdered 
limestone  or  shale,  blast-furnace  slag,  hydraulic  lime, 
trass,  etc.  The  nature  of  the  tests  depends  upon  that 
of  the  adulteration  to  be  discovered. 

The  specific-gravity  test  is  sometimes  utilized  for 
this  purpose,  the  foreign  matter  being  lighter  than 
cement.  The  differences,  however,  are  so  small  that 
the  test  at  best  is  a  rather  uncertain  one. 


208  HYDRAULIC  CEMENT. 

The  determination  of  the  loss  upon  ignition  may 
show  the  presence  of  foreign  matter  containing  vola- 
tile elements,  while  chemical  analysis,  separating  the 
fine  and  coarse  parts  of  the  cement  and  comparing  the 
results,  is  sometimes  resorted  to,  as  stated  in  Art.  63. 

Microscopic  Test. — The  use  of  the  microscope  for 
the  purpose  of  determining  the  character  of  the  sub- 
stances present  in  cement  has  often  been  proposed. 
Prof.  Le  Chatelier  made  a  careful  study  of  Portland 
cement  by  examining  sections  of  unground  clinker 
by  polarjscopic  analysis.  He  thus  demonstrated  the 
possibilities  of  this  method  in  the  scientific  investiga- 
tion of  the  nature  of  the  material. 

This  method  is  not,  however,  applicable  as  a  test 
for  homogeneity.  Attempts  have  also  been  made  to 
determine  the  character  of  the  cement  by  studying 
the  grains  of  which  the  powder  is  composed  under  the 
microscope.  For  Portland  cement,  it  has  been  ob- 
served that  the  active  portion  of  the  cement  is  com- 
posed of  grains  of  angular  form  and  metallic  lustre, 
and  that  the  parts  of  earthy  appearance  are  probably 
inert.  It  has  also  been  found  that  the  color  of  the 
grains  seems  to  bear  some  relation  to  their  value  in 
the  cement.  Further  study  may  reveal  more  positive 
indications  of  value  based  upon  the  microscopic  ap- 
pearance, but  it  seems  unlikely  that  this  method  will 
be  applied  to  the  determination  of  value  in  practice. 

For  tests  of  homogeneity,  the  employment  of  an 
ordinary  magnifying-glass  may  perhaps  give  useful 
results.  M.  Feret,  who  made  a  study  of  the  matter 
and  presented  a  report  to  the  French  Commission  upon 
Methods  of  Testing  Materials,  recommends  that  the 


SPECIAL  TESTS.  2OQ 

material  to  be  examined  be  sifted  through  the  sieve 
of  4900  meshes  per  square  centimeter  and  the  portion 
retained  by  that  sieve  be  used  in  the  examination,  on 
account  of  the  difficulty  of  observing  the  grains  when 
mixed  with  the  impalpable  powder.  It  is  also  sug- 
gested that  two  glasses  be  used :  the  first  of  a  power 
of  about  three  diameters  to  examine  the  general 
appearance  and  uniformity  of  the  material;  the  second 
of  about  eight  diameters  to  study  in  detail  the  various 
grains.  The  material  is  placed  upon  a  black  surface 
to  be  examined.  The  points  to  be  noticed  are  the 
form,  color,  and  transparence  of  the  grain  and  the 
appearance  of  its  fracture.  It  is  also  desirable  to  test 
the  hardness  with  a  steel  point  and  the  solubility  in  a 
drop  of  water  or  acid.  It  is  to  be  borne  in  mind  that 
the  character  of  the  material  in  the  coarse  particles  is 
not  necessarily  the  same  as  in  the  finer  portions,  or  at 
least  the  proportions  of  the  various  ingredients  may 
not  be  the  same. 

M.  Feret  found  that  pure  cement,  thoroughly  well 
burned,  gave  "  grains  all  of  the  same  appearance, 
black,  opaque,  angular,  hard,  and  with  a  rough  frac- 
ture. Mixed  with  a  drop  of  water  they  show  at  first 
no  change,  but  after  several  minutes  a  sort  of  halo 
appears,  produced  by  the  beginning  of  crystallization 
of  the  soluble  compounds.  These  grains  color  im- 
mediately in  hydrochloric  acid  to  a  yellow,  but  are 
completely  dissolved  with  difficulty. 

"  Rock  less  burned  gives  grains  equally  opaque, 
but  of  color  less  deep,  varying  to  brown,  gray,  or 
green.  The  underburned  rock  gives  gray  or  yellow 
grains,  which  crush  easily  under  the  point  of  a  knife, 


210  HYDRAULIC   CKMENT. 

and  are  attacked  by  acids  with  the  disengagement  of 
carbonic  acid." 

"  When,  instead  of  material  prepared  in  the  labo- 
ratory and  thoroughly  homogeneous,  the  residue  ob- 
tained from  market  grades  of  cement  is  used,  the 
appearance  is  very  different  even  if  the  material  be  of 
best  quality.  The  color  is  less  deep  and  the  material 
appears  very  heterogeneous.  Such  cements  contain 
always,  with  many  of  these  black,  brown,  or  green 
grains,  a  large  number  of  more  vitreous  material, 
green,  yellow,  and  white,  without  containing  foreign 
matter." 

"  When  the  cement  is  less  well  burned  the  color 
of  the  large  grains  becomes  more  clear,  and  the  glass 
shows  an  increasing  number  of  gray  friable  grains,  the 
black  grains  decreasing  in  number." 

"  It  is  not  uncommon  to  find  in  the  cement  clinker 
pieces  of  bright  colors,  blue,  green,  violet,  red,  and 
white;  these  materials  are  usually  soft  and  porous." 

"  Carbon  in  black  and  brilliant  grains,  with  con- 
choidal  fracture,  is  found  in  all  the  specimens,  and 
easily  known." 

"  The  debris  of  flint  from  the  millstones  is  not 
easily  distinguished  from  certain  underburned  cement 
grains;  they  are  the  gray  morsels,  hard  and  opaque. 
They  differ  from  the  cement  grains  in  not  being 
attacked  by  water  or  acids." 

"  The  appearance  of  grains  of  slag  vary  according 
to  the  nature  of  the  slag.  Commonly,  the  grains  are 
compact,  of  a  bluish  gray  color,  and  smooth  clean 
fracture.  Sometimes  the  grains  are  vitreous  and 
black.  The  granular  slags  employed  in  making  slag- 


SPECIAL  TESTS.  211 

cements  are  soft,  and  leave  few  grains.  Their  debris 
has  the  appearance  of  colorless  glass,  or  tint  of  yellow 
or  green,  and  fractures  easily  under  the  point  of  a 
knife." 

"  Grappiers  give  round  grains,  usually  more  clear 
in  color  than  the  grains  of  cement." 

"  Gypsum  added  to  cement  clinker  before  grinding 
may  show  large  white  crystalline  grains  easily  seen. 
They  may  be  identified  by  their  hardness  and  solu- 
bility. Plaster  is  difficult  to  recognize,  because  it 
grinds  fine  and  leaves  no  crystals." 

When  plaster  has  been  added  to  cement,  it  may 
sometimes  be  detected  by  separate  analyses  of  the 
fine  and  coarse  parts,  as  to  sulphuric  acid.  The  fine 
parts  containing  the  plaster  give  the  higher  results. 

Le  Cliatclicr 's  Test. — This  method  of  detecting 
adulteration,  proposed  by  Prof.  Le  Chatelier,  consists 
in  forming  a  liquid,  by  the  mixture  of  methylene 
iodide  and  benzine,  of  density  slightly  below  that  of 
cement  and  above  that  of  slag,  and  separating  by  its 
means  the  cement  from  the  adulteration.  It  is  thus 
described  by  Prof.  Le  Chatelier: 

"  The  first  operation  is  the  preparation  of  a  liquid 
of  proper  density  for  the  separation, — 2.95  for  exam- 
ple. In  this  liquid  the  cement  sinks  to  the  bottom 
and  the  slag  floats  on  the  surface.  To  prepare  the 
liquid  add  to  the  methylene  iodide  of  density  3.1  a 
small  quantity  of  benzine,  stopping  the  moment  a 
crystal  of  aragonitc  of  density  2.94  just  remains  at  the 
surface.  It  is  well  not  to  make  the  mixture  directly, 
but  to  make  two  mixtures — the  one  a  little  lighter, 
the  other  a  little  heavier,  than  the  density  sought; 


212 


HYDRAULIC   CEMENT. 


thus  obtaining  a  more  progressive  variation,  and  more 
easily  regulated." 

"  The  apparatus  consists  of  a  glass  tube  (Fig.  30), 
10   millimeters    in    diameter,    70    millimeters    high, 


FIG.  30. 

widened  into  a  funnel  at  top  and  terminated  at  bottom 
in  a  point,  with  an  orifice  I  millimeter  in  diameter. 
This  orifice  is  closed  on  the  interior  a  little  above  the 
bottom,  by  a  small  emery  stopper,  fastened  to  a  long 
glass  rod,  which  issues  from  the  top  of  the  tube. 

"  To  make  an  experiment,  the  stopper  is  wet  with 
water  (grease  is  dissolved  by  the  liquid),  to  prevent 
leakage.  Two  grammes  of  cement  are  introduced, 
then  five  cubic  centimeters  of  liquid  (density  2.95). 
It  is  then  agitated  in  a  lively  manner  with  a  small 


SPECIAL  TESTS.  21$ 

platinum  thread  bent  around  into  a  hook,  in  order  to 
drive  out  the  bubbles  of  air  and  thoroughly  mix  the 
cement  in  suspension  in  the  liquid.  Finally,  it  is 
allowed  to  settle  for  an  hour;  after  that  time  there 
is  formed  two  layers — the  cement  at  the  bottom  and 
the  slag  at  the  top.  The  stopper  of  emery  is  lightly 
raised  by  the  rod  to  which  it  is  attached,  letting  out 
the  cement  and  part  of  the  liquid,  and  is  then  replaced. 
The  cement  is  caught  upon  a  filter,  through  which 
the  liquid  passes  into  a  flask,  when  it  is  ready  for 
another  operation. 

"  The  slag  and  remainder  of  the  liquid  is  received 
upon  another  filter.  Finally,  the  tube  and  filters  are 
washed  with  benzine  and  dried;  the  cement  and  slag 
are  weighed,  and  analyzed  chemically  if  thought 
proper." 

The  cost  is  said  to  be  the  principal  objection  to  this 
method,  although  but  a  small  quantity,  a  part  of  a 
cubic  centimeter  of  iodide  of  methylene,  is  required 
for  each  operation. 

ART.  65      ABRASIVE  TESTS. 

Cement  to  be  used  for  sidewalks,  floors,  or  artificial 
stone  is  sometimes  submitted  to  tests  for  resistance  to 
abrasion.  This  test  is  frequently  employed  in  Ger- 
many, the  apparatus  designed  by  Prof.  Bauschinger 
being  used.  This  apparatus  consists  of  a  cast-iron 
disk  122  centimeters  in  diameter  and  3  centimeters 
thick,  mounted  to  rotate  horizontally  at  about  20 
revolutions  per  minute.  Specimens  6x6,  10  X  10, 
or  12  X  12  centimeters  in  section  are  employed. 


2I4 


HYDRAULIC   CEMENT. 


They  are  held  upon  the  disk  with  a  pressure  of  30 
kilogrammes,  and  20  grammes  of  standard  sand  are 


FIG.  31. 

added  for  each  10  turns.     200  turns  are  given,  and 
the  loss  in  weight  of  the  specimen  is  determined. 
Fig.    31    shows   a   similar  apparatus   made   by  the 


SPECIAL  TESTS.  21$ 

Riehle  Bros.  Testing-machine  Co.,  and  used  for  brick 
and  stone  tests.  Abrasion  tests,  when  employed,  are 
usually  made  for  both  neat  cement  and  sand-mortar. 
The  test  of  mortar  as  used  in  practice  is  evidently  the 
more  important.  Resistance  to  abrasion  varies  with 
the  character  of  sand  used,  and  for  sand-mortar  de- 
pends upon  the  adhesion  of  the  cement  to  the  sand 
and  the  hardness  of  the  grains  of  sand.  Sand-mor- 
tars with  moderate  proportions  of  sand  give  better 
resistance  to  abrasion  than  neat  cement. 

ART.  66.     TESTS  FOR  POROSITY. 

Tests  for  the  porosity  of  mortar  are  interesting  in 
studying  the  properties  of  the  materials  and  methods 
of  gauging  them.  The  porosity  may  often  be  a  matter 
of  importance  as  affecting  the  durability  of  mortar 
subjected  to  the  action  of  disintegrating  agencies. 
These  tests  are  not  employed  for  the  reception  of 
material.  The  porosity  depends  to  a  much  greater 
extent  upon  the  quantity  of  water  used  in  gauging, 
and  the  degree  of  compression  used  in  forming  the 
briquette,  than  upon  the  character  of  the  cement  or 
sand  employed,  although  probably  the  fineness  of 
these  materials  has  some  influence. 

The  test  for  porosity  consists  in  determining  the 
ratio  of  the  volume  of  voids  to  the  total  volume  of  the 
mortar.  The  difficulty  of  determining  when  the  voids 
are  completely  filled  with  liquid,  or  when  the  mortar 
is  quite  dry,  makes  the  process  a  somewhat  uncertain 
one,  and  requires  that  a  definite  procedure  be  followed 
in  order  to  arrive  at  concordant  and  comparable 
results. 


2l6  HYDRAULIC  CEMENT. 

The  method  usually  followed  is  to  measure  the  total 
apparent  volume  and  the  volume  of  material:  the 
volume  of'  voids  is  then  the  difference  of  the  two; 
this  divided  by  total  volume  is  the  percentage  of 
porosity.  To  measure  the  total  apparent  volume, 
the  simplest  method  is  to  make  the  block  of  such  form 
that  it  may  be  directly  measured.  When  this  method 
is  not  employed  the  total  volume  may  be  obtained  by 
weighing  the  block  in  a  saturated  condition  in  water 
and  in  the  air;  the  difference  between  the  two  weights 
is  the  weight  of  water  displaced,  from  which  the 
volume  may  be  found.  In  order  to  obtain  the  same 
state  of  saturation  the  weight  in  water  should  be  taken 
immediately  before  that  in  air.  Grease  is  also  some- 
times applied  to  the  surface  of  the  block  to  prevent 
change  during  the  weighing. 

To  obtain  the  volume  of  solid  material  in  the  block, 
the  difference  between  the  weight  of  the  block  when 
dry,  in  air,  and  of  the  saturated  block  in  water  is 
obtained.  This  difference  is  the  weight  of  water  dis- 
placed by  solid  material.  To  secure  good  results  the 
entire  dryness  in  the  first  instance  and  the  complete 
saturation  in  the  second  is  essential.  The  block  may 
be  placed  in  warm  dry  air  for  a  period  sufficient  to 
permit  the  weight  to  become  constant.  For  this  pur- 
pose it  is  necessary  that  the  temperature  be  the  same 
in  all  cases,  as  the  amount  of  hygrometric  water  given 
off  depends  upon  the  temperature  of  drying;  100°  to 
I  IO°  Fahr.  has  been  sometimes  employed,  and  is 
recommended  by  the  French  Commission  on  Standard 
Tests.  After  the  dry  weight  is  obtained,  considerable 
difficulty  may  be  experienced  in  getting  complete 


SPECIAL   TESTS.  2 1/ 

saturation.  If  the  block  be  simply  immersed,  air  will 
be  retained  in  the  voids,  and  a  long  period  required 
to  obtain  a  constant  weight.  Boiling  is  sometimes 
resorted  to,  but  has  the  disadvantage  of  perhaps  caus- 
ing change  of  volume  in  the  mortar.  The  best  method 
of  expediting  the  test  is  to  exhaust  the  air  by  placing 
the  specimen  in  water  under  the  receiver  of  an  air- 
pump. 

Prof.  Tetmajer  recommends*  that  a  temperature  of 
1 10°  C.  be  used  in  drying,  and  that  the  volume  of  solid 
matter  be  obtained  by  weighing  dry  in  air  and  satu- 
rated in  paraffine,  and  determining  the  volume  of 
paraffine  displaced.  The  block  is  then  put  in  water, 
and  the  total  volume  obtained  by  measuring  directly 
the  volume  of  water  displaced.  For  this  purpose  an 
apparatus  is  employed  which  is  very  similar  to  the 
Schuman  volumenometer,  Fig.  5,  but  with  a  remov- 
able cover  to  the  dish  to  admit  the  specimen. 

ART.  67.     TESTS  FOR  PERMEABILITY. 

The  permeability  of  mortar  is  quite  distinct  from 
its  porosity,  and  the  more  porous  is  not  necessarily  the 
more  permeable.  Tests  for  permeability,  like  those 
for  porosity,  are  interesting  and  important  in  the 
studies  of  the  properties  of  mortar,  but  are  not  suitable 
for  use  in  specifications  for  the  reception  of  material. 
The  common  test  for  permeability  is  made  by  forcing 
water  through  a  cake  of  mortar  under  pressure.  This 


*  Methoden    und    Resultate    der    Priifung  der    Hydraulischen 
Bindemittei  (Zurich,  1893). 


2l8  HYDRAULIC   CEMENT. 

may  be  accomplished  either  by  subjecting  the  mortar 
directly  to  the  pressure  of  a  considerable  head  of 
water,  or  by  subjecting  the  block  of  mortar  to  a  small 
pressure  from  a  column  of  water  above,  while  the  air 
is  exhausted,  forming  a  partial  vacuum  below.  The 
latter  method  has  been  usually  preferred  in  Europe, 
although  the  former  has  been  made  standard  in  France. 

The  apparatus  shown  in  Fig.  32  has  been  frequently 
employed  in  these  tests.  It  consists  of  a  heavy  cylin- 
drical glass  jar  (a)  with  a  ground  upper  edge,  upon 
which  is  accurately  fitted  the  second  cylinder  (*/). 
The  specimen  (c),  having  a  section  of  20  square  centi- 
meters and  a  thickness  of  I  centimeter,  is  fastened  and 
made  water-tight  in  the  cylinder  (d)  by  means  of  a 
rubber  packing-ring.  A  ground-glass  stopper  covers 
the  cylinder  (b)  and  carries  the  graduated  tube  (e), 
which  has  a  capacity  of  200  cubic  centimeters  and  is 
graduated  to  1/2  centimeter.  The  space  under  the 
specimen  is  connected  with  an  air-pump  and  a  mer- 
cury manometer,  a  stop-cock  being  placed  in  the  tube 
connecting  with  the  air-pump.  In  using  the  appa- 
ratus, after  the  specimen  has  been  placed  in  the  cylin- 
der and  the  cover  clamped  down,  the  air  is  exhausted 
from  a,  the  stop-cock  closed,  and  the  graduated  tube 
filled  with  water  to  the  zero  mark.  The  quantity  of 
water  percolating  through  the  specimen  may  then  be 
read  from  the  scale  for  any  desired  unit  of  time. 

The  arrangement  shown  in  Fig.  33  is  also  used  to 
some  extent  in  Europe.  It  consists  of  a  hollow 
cylindrical  block,  1 10  millimeters  in  diameter  and  200 
millimeters  high,  of  the  mortar  to  be  tested,  into  the 
top  of  which  a  glass  tube  is  set  with  neat  cement.  In 


SPECIAL  TESTS. 


2I9 


making  the  test  a  rubber  tube  is  connected  with  the 
glass  tube  and  with  a  vessel  placed  at  such  an  eleva- 


FIG.  32. 


FIG.  33 


tion   as  will  give  the  pressure  desired,   which  varies 
according  to  the  mortar  to  be  tested. 

A  cubical  block,  arranged  as  shown  in  Fig.  34,  is 


220 


HYDRAULIC  CEMENT. 


also  frequently  employed.  For  this  purpose  the 
standard  block  as  used  for  compressive  tests  may  be 
employed.  This  form  is  recommended  by  the  French 


FIG.  34. 

Commission  upon  Methods  of  Testing  Materials,  as 
follows: 

"  The  permeability  of  cements  and  mortars  may  be 
expressed  by  the  number  of  liters  of  water  which 
traverse  a  cube  with  faces  of  50  square  centimeters 
during  a  given  time. 

"  The  water  is  supplied  by  a  glass  tube  35  mil- 
limeters in  diameter  and  no  millimeters  high,  sealed 
vertically  by  the  aid  of  neat  cement  upon  the  upper 
face  of  the  block.  The  upper  end  of  the  tube  is  con- 
nected by  a  rubber  tube  with  a  reservoir  raised  to  an 
elevation  corresponding  to  the  head  desired.  The 
heads  adopted,  according  to  the  permeability  of  the 
mortar,  are  o.  10  meter,  I  meter,  and  10  meters. 

"  Before  the  test  is  made,  the  blocks  should  be  im- 
mersed for  48  hours,  with  such  precautions  as  are 
necessary  to  secure  as  complete  saturation  as  possible. 


SPECIAL  TESTS.  221 

After  beginning  the  experiment  the  block  is  kept 
completely  immersed." 

"  The  rate  of  filtration  is  determined  after  24  hours, 
7  days,  28  days,  3  months." 

' '  The  determinations  are  made  for  three  blocks,  the 
mean  results  being  taken  for  the  two  blocks  most  con- 
cordant." 

"  The  standard  test  for  permeability  is  to  be  made 
upon  standard  plastic  mortar  28  days  old,  kept  under 
water. ' ' 

"  For  tests  upon  mortars  of  different  ages  and  com- 
positions, it  is  recommended  to  employ  i  to  2  and  I 
to  5  mortars  made  plastic,  and  7  days,  28  days,  and  3 
months  old." 

The  permeability  of  mortars  to  gases  is  a  matter 
upon  which  experiments  are  very  desirable,  but  con- 
cerning which  comparatively  little  is  known. 

ART.  68.     FROST  TESTS. 

Tests  are  frequently  made  upon  cement-mortars  to 
determine  the  effect  of  freezing  before  setting  or  while 
the  mortar  is  still  comparatively  fresh,  for  the  purpose 
of  investigating  the  safety  of  using  the  mortar  in  freez- 
ing weather,  or  the  best  method  of  so  using  it. 

These  tests  are  usually  made  by  exposing  briquettes 
to  freezing  temperatures,  either  by  taking  advantage 
of  natural  low  temperatures,  or  by  using  a  freezing 
mixture,  and  comparing  the  results  of  tensile  tests 
upon  briquettes  so  treated  with  those  kept  under  nor- 
mal conditions. 

Tests  of  this  kind  may  be  of  much  value  in  showing 


222  HYDRAULIC   CEMENT. 

the  relative  properties  of  various  materials,  and  often 
give  very  interesting  results.  They  are  to  be  used 
with  caution,  however,  in  determining  from  them  the 
probable  effect  of  freezing  upon  work  in  which  the 
mortar  may  be  used.  Frequently  the  results  of 
briquette  tests,  and  the  action  of  the  material  in  large 
masses  in  construction  are  not  concordant.  Injury  to 
work  may  perhaps  result  not  only  from  the  injurious 
effect  of  frost  upon  the  strength  of  the  material,  but 
also  from  expansive  action  upon  the  mass  of  mortar, 
after  setting,  while  still  too  weak  to  offer  effectual 
resistance  to  distortion. 

ART.  69.     TEST  FOR  YIELD  OF  MORTAR. 

In  some  laboratories  it  is  the  custom  to  make  tests 
of  the  yield  of  mortar  obtained  from  given  weights  of 
the  materials  employed.  This  may  sometimes  be  of 
importance  as  affecting  the  economy  of  use  of  various 
materials,  while  a  study  of  the  differences  obtained 
with  different  material  is  interesting. 

In  conducting  such  tests  it  is  evidently  necessary 
to  adopt  a  standard  method  of  gauging  the  ingredients, 
the  volume  of  the  resulting  product  being  much 
affected  by  variations  in  manipulation.  The  method 
employed  is  usually  to  measure  directly  the  volume 
of  paste  obtained  by  mixing  to  standard  consistency  a 
unit  weight  of  neat  cement  or  of  cement  and  sand  in 
proper  proportions.  For  this  purpose  the  paste  is  put 
in  a  graduated  glass  cylinder,  care  being  taken  to 
eliminate  all  of  the  air-bubbles. 

Sometimes  the  test  is  made  by  making  blocks  of  the 


SPECIAL  TESTS.  22$ 

paste,  which  are  allowed  to  set,  their  volumes  being 
subsequently  obtained  by  greasing  their  surfaces  and 
taking  the  difference  of  weight  in  air  and  water. 

ART.  70.     TESTS  OF  SAND. 

Tests  of  the  sand  to  be  used  in>  mortar  are  of  much 
value  in  determining  the  relative  value  of  different 
sands,  as  well  as  in  studying  the  effect  of  variations  in 
the  nature,  form,  or  size  of  grains  of  which  it  may  be 
composed. 

Complete  tests  should  include  an  examination  of  the 
nature  of  the  sand,  its  fineness  as  shown  by  the 
amount  retained  by  various  sieves;  the  form  of  grain, 
which  may  be  examined  under  a  glass;  its  specific 
gravity  or  the  weight  of  a  unit  volume;  its  minera- 
logical  character.  Tests  of  the  tensile  strength  of 
mortar  made  from  the  sand  to  be  tested  as  compared 
with  similar  tests  made  upon  standard  sand  are  of 
most  importance  as  indicating  the  value  of  the  sand  to 
combine  with  cement  in  forming  mortar. 


CHAPTER    IX. 
CEMENT-MORTAR   AND   CONCRETE. 

ART.  71.     SAND  FOR  MORTAR. 

As  hydraulic  cement  is  commonly  mixed  with  cer- 
tain proportions  of  sand,  when  used  in  construction, 
the  nature  and  quantity  of  sand  used,  and  the  method 
of  manipulating  the  materials  in  forming  the  mortar, 
have  nearly  as  important  an  effect  upon  the  final 
strength  of  the  work  as  the  quality  of  cement  itself. 

In  testing  cement,  a  standard  sand  is  usually  em- 
ployed. This  sand  may  be  obtained  quite  uniform  in 
quality.  In  the  execution  of  work,  however,  local 
sand  must  generally  be  employed ;  this  varies  widely 
in  character,  and  should  always  be  carefully  considered 
upon  any  important  work,  where  the  development  of 
strength  and  lasting  qualities  in  the  mortar  is  of  im- 
portance. 

The  importance  of  the  quality  of  sand  in  mortar  is 
not  commonly  appreciated,  and  but  little  attention  is 
usually  given  to  securing  good  sand  even  when  the 
cement  is  subjected  to  rigid  requirements. 

Mr.  Newman,  in  his  book  on  concrete,  in  speaking 
of  the  materials  used  in  concrete,  says:  "  Considering 
the  very  varied  character  of  sand  and  gravel,  it  seems 
that  more  attention  should  be  given  to  the  particu- 

224 


CEMENT-MORTAR   AND   CONCRETE.  22$ 

larization  of  the  sand  and  gravel,  remembering  the 
locality  of  the  work  in  each  case,  and  the  geological 
features  of  the  district  from  which,  for  reasons  of 
economy,  the  sand  or  gravel  must  be  obtained. 

"  The  value  of  it  from  an  engineering  point  of  view 
may  be  very  different,  even  in  a  small  area;  and  to 
be  most  particular  as  to  the  character  and  quality  of 
Portland  cement,  and  apparently  regardless  of  that  of 
the  sand  and  gravel,  although  the  latter  form  85$  to 
93$  of  the  volume  of  concrete  at  the  time  of  mixing, 
is  hardly  capable  of  vindication,  especially  as  Portland- 
cement  concrete  should  be  a  monolithic  mass,  and  the 
effect  of  sand  is  to  retard  induration  and  decrease 
strength." 

The  chemical  nature  of  the  sand  does  not  appear  to 
have  any  important  bearing  upon  its  usefulness  in 
mortar.  Silicious  sand  is  sometimes  thought  to  exer- 
cise a  slow  puzzolanic  action,  and  perhaps  aid  some- 
what in  the  final  hardening  of  the  mortar.  It  is 
usually  the  best  sand  for  the  purpose.  Calcareous 
sands  are  good,  if  not  friable  or  composed  of  soft  par- 
ticles. Argillaceous  sand  is  usually  less  desirable,  and 
has  been  found  in  some  instances  apparently  to  cause 
ultimate  disintegration  in  sea-water,*  although  a  small 
admixture  of  clay  in  the  sand  may  not  be  objection- 
able, and  has  been  shown  in  some  instances  not  to 
decrease  the  strength  when  present  to  an  extent  not 
exceeding  10$  of  the  sand. 

A  sand  for  use  in  mortar  should  be  clean,  and  as 
free  from  loam,  mud,  or  organic  matter  as  possible. 

*Annales  des  Fonts  et  Chaussees,  1890,  vol.  II.  p.  277. 


226  HYDRAULIC   CEMENT. 

In  general,  the  presence  of  any  foreign  matter  is  to  be 
avoided. 

The  sand  should  also  be  as  sharp  as  possible ;  if  it 
be  composed  of  angular  grains,  it  will  compact  much 
closer  and  make  a  stronger  mortar  when  used  with  the 
same  proportion  of  cement  than  if  it  be  composed  of 
rounded  grains. 

Coarse  sand  is  usually  preferable  to  that  which  is 
very  fine,  provided  it  be  fine  enough  to  give  a  smooth 
mortar,  as  it  gives  better  strength.  The  coarse  sand 
presents  less  surface  to  be  coated  with  cement,  and 
the  interstices  are  more  easily  filled.  Fine  cand 
requires  more  water  in  mixing  in  order  to  arrive  at 
the  same  consistency,  and  thus  gives  usually  a  more 
porous  mortar.  Fine  sand  may,  however,  be  desirable 
when  an  impervious  mortar  is  the  object. 

The  use  of  a  mixture  of  grains  of  various  sizes  is 
usually  desirable,  as  giving  less  voids  to  be  filled  by 
the  cement ;  and  it  is  frequently  found  that  when  the 
cement  is  not  in  considerable  excess  the  strength 
obtained  by  such  a  mixture  is  much  greater  than  is 
given  by  either  the  large  or  small  grains  alone. 

This  is  doubtless  due  to  the  voids  in  the  sand  being 
more  completely  filled  by  the  cement.  Large  grains 
of  uniform  size  seem  desirable  where  a  meagre  mortar 
is  to  be  employed,  the  quantity  of  cement  being  insuffi- 
cient to  fill  the  voids  and  only  used  to  coat  the  grains 
and  cement  them  together. 

Fine  sand  is  objectionable  in  mortar  exposed  to  the 
action  of  sea-water  on  account  of  the  increased  poros- 
ity. 

In  using  quick-setting  cement  the  drvness  of  thp 


CEMENT-MORTAR   AND   CONCRETE.  22? 

sand  is  a  matter  of  importance;  if  the  sand  be  damp, 
when  the  mixture  of  sand  and  cement  is  made,  suffi- 
cient moisture  may  be  given  off  to  induce  hydration 
previous  to  the  addition  of  the  water.  With  slow 
cements  this  is  of  less  consequence. 

M.-  Candlot  found  *  cement  left  in  contact  with  sand 
which  was  slightly  damp,  not  sufficiently  so  to  cause 
the  cement  to  set,  was  greatly  modified  in  action, 
probably  through  the  hydration  of  the  aluminate  of 
lime. 

Cement  left  ten  minutes  in  contact  with  sand  con- 
taining 3$  of  moisture,  and  then  sifted  out,  had  its 
time  of  setting  increased  from  a  few  minutes  to  several 
hours.  When  the  sand  was  very  wet,  the  action  was 
more  serious  and  a  loss  of  strength  resulted. 

ART.  72.     PROPORTIONING  MORTAR. 

The  relative  proportions  of  the  ingredients  to  be 
used  in  mortar  are  usually  stated  as  a  ratio  of  parts  of 
cement  to  sand,  and  the  quantities  are  determined 
either  by  weight  or  volume.  Cement  should  always 
be  measured  by  weight  on  account  of  the  variation  in 
volume  caused  in  packing,  and  the  difficulty  of  meas- 
uring by  volume  always  in  the  same  way,  while  the 
sand  may  conveniently  be  measured  by  volume. 

The  proportions  of  sand  and  cement  to  be  used  in 
any  instance  depends  upon  the  nature  of  the  work 
ind  the  necessity  for  the  development  of  strength  or 
imperviousness  in  the  mortar.  The  volume  of  in- 

*  Ciment  et  Chaux  hydrauliques  (Paris,  1891). 


228  HYDRAULIC   CEMENT. 

terstices  to  be  filled  varies  with  the  forms  and  sizes  of 
the  grains  of  sand,  and  the  quantity  of  cement  neces- 
sary to  reach  the  same  strength  with  different  sands 
varies  considerably.  The  volume  of  a  given  weight 
of  sand  is  also  greater  when  damp  than  when  dry,  and 
the  same  proportion  to  a  given  volume  of  sand  gives 
a  richer  mortar  when  the  sand  is  measured  in  a  damp 
condition  than  when  measured  dry. 

The  proportions  most  commonly  used  in  ordinary 
work  are,  for  natural  cements,  one  part  cement  to  one 
or  sometimes  two  parts  sand,  and  for  Portland  cement 
one  part  cement  to  three  parts  sand.  If  the  propor- 
tions for  the  mixture  were  regulated  by  the  value  of 
the  sand  the  interests  of  economy  might  frequently 
require  changes  in  proportions,  and  would  usually 
demand  the  use  of  the  best  sand  obtainable. 

Good  sand  in  a  I  to  3  mixture  frequently  gives 
greater  strength  than  a  poorer  one  mixed  I  to  2,  and 
either  mortar  may  give  equally  good  results  in  practice. 

The  cement  in  mortar  must,  for  the  best  results, 
both  coat  the  grains  of  sand  so  as  to  cause  them  to 
adhere  to  each  other,  and  fill  the  voids  between  them. 
Mortar  to  be  exposed  to  the  action  of  water,  particu- 
larly sea-water,  should  always  contain  a  surplus  of 
cement  over  what  is  necessary  to  fill  the  voids  in  the 
sand. 

M.  Candlot  gives  as  a  minimum  for  mortar  to  be 
used  in  sea-water  a  proportion  of  600  kilogrammes  of 
cement  to  a  cubic  metre  of  sand,  which  is  to  be  in- 
creased when  the  cement  is  not  finely  ground. 

Fine  sand  is  to  be  avoided,  if  possible;  when  used, 
the  proportion  of  cement  to  be  increased. 


CEMENT-MORTAR   AND   CONCRETE.  22Q 

The  complete  filling  of  the  voids  in  the  sand  so  as 
to  exclude  the  water  from  the  interior  of  the  mass  and 
prevent  the  action  of  the  magnesian  salts  upon  the 
cement  is  in  such  work  a  matter  of  first  importance. 

When  the  mortar  is  to  be  subjected  to  the  action  of 
fresh  water  its  permeability  may  not  be  a  matter  of 
so  great  consequence,  and  in  many  instances  less  rich 
mortar  may  frequently  be  used  to  advantage,  provided 
sufficient  strength  be  obtained  for  the  given  purpose. 
The  carbonizing  of  the  lime  forms  a  protection  to  the 
mass  of  mortar,  which  is  not  subject,  as  in  sea-water, 
to  the  action  of  the  magnesian  salts. 


ART.  73.     GAUGING  MORTAR. 

In  mixing  cement-mortar,  the  cement  and  sand  are 
first  thoroughly  mixed  dry,  the  water  then  added,  and 
the  whole  worked  to  a  uniformly  plastic  condition. 
The  value  of  the  mortar  will  depend  upon  the 
thoroughness  of  the  operation;  the  cement  must  be 
uniformly  distributed  through  the  sand  during  the  dry 
mixing,  while  thoroughly  working  the  mass  after  the 
addition  of  the  water  will  greatly  increase  its  strength. 
In  mixing  by  hand,  by  the  ordinary  method,  a  plat- 
form or  box  is  used ;  the  sand  and  cement  are  placed 
upon  the  platform  in  layers,  with  a  layer  of  sand  at 
bottom,  and  then  turned  and  mixed  with  shovels  until 
properly  distributed  through  the  mass.  The  material 
is  then  formed  into  a  ring,  or  a  mound  with  a  crater 
at  the  centre,  and  all  the  water  necessary  added  at 
once,  after  which  the  material  is  thrown  up  from  the 


230  HYDRAULIC   CEMENT. 

sides  until  the  water  is  all  taken  up,  and  then  worked 
into  a  plastic  condition. 

In  order  to  secure  proper  manipulation  of  the  ma- 
terials on  the  part  of  the  workmen,  it  is  quite  common 
to  require  that  the  whole  mass  shall  be  turned  over  a 
certain  number  of  times  with  the  shovel,  both  dry  and 
wet. 

The  mixing  should  be  quickly  and  energetically 
done,  only  such  quantity  being  mixed  at  once  as  can 
be  used  before  the  initial  set  of  the  mortar  takes 
place. 

The  cement  should  not  be  left  in  contact  with  the 
sand  for  any  considerable  time  before  being  used,  or  a 
considerable  quantity  should  not  be  mixed  dry  and 
left  to  stand  until  wanted,  as  the  moisture  commonly 
in  the  sand  will  to  some  extent  act  upon  the  cement. 

Upon  large  works  mechanical  mixers  are  frequently 
employed,  with  the  advantage  of  greatly  lessening  the 
labor  of  manipulating  the  material,  and  also  of  insur- 
ing thorough  mixing. 

The  quantity  of  water  to  be  used  in  gauging  mortar 
can  be  determined  only  by  experiment  in  each  instance. 
It  depends  upon  the  nature  of  the  cement  and  sand, 
and  upon  the  proportion  of  sand  to  cement.  The 
water  may  be  considered  as  made  up  of  two  parts — 
that  necessary  to  gauge  the  neat  cement  to  a  paste, 
and  that  required  to  wet  the  surfaces  of  the  sand. 
The  first  varies  directly  with  the  quantity  of  cement, 
the  second  with  that  of  the  sand.  Fine  sand  requires 
more  water  than  coarse  sand  to  reach  the  same  con- 
sistency, and  mortar  of  fine  sand  should  be  made  a 
little  more  wet  than  when  of  coarse  sand,  to  give  the 


CEMENT-MORTAR  AND   CONCRETE.  23! 

best  results  in  practice.  The  quantity  of  water  also 
varies  with  the  dryness  of  the  sand  and  its  porosity. 

The  amount  of  water  to  be  used  in  mixing  mortar 
for  ordinary  masonry  is  such  that  the  mortar  when 
properly  mixed  shall  have  a  stiff  plastic  condition.  It 
should  not  be  a  soft,  semi-fluid  mass.  The  proper 
consistency  is  described  by  M.  Candlot  as  such  that  if 
a  ball  of  mortar  be  formed  in  the  hand  and  allowed  to 
fall  through  a  small  height,  it  should  neither  lose  its 
form  nor  crack;  the  ball  should  not  be  wet  enough 
to  stick  to  the  hand.  The  best  results  are  usually 
obtained  by  mixing  with  as  little  water  as  will  admit 
of  proper  manipulation  in  the  work,  and  wetting  the 
surfaces  with  which  it  is  to  be  in  contact. 

In  all  cases  the  proper  quantity  of  water  should 
first  be  determined  by  experiment,  and  afterward,  in 
preparing  the  mortar  for  use  in  work,  the  required 
quantity  should  each  time  be  added  by  measurement. 
The  addition  of  water  little  by  little,  or  from  a  hose, 
should  never  be  allowed. 

ART.  74.     PREPARATION  OF  CONCRETE. 

Concrete  is  any  mixture  of  mortar  with  coarse 
material,  usually  gravel  or  broken  stone,  the  office  of 
the  mortar  being  to  bind  together  the  pieces  of  the 
aggregate  and  fill  the  spaces  between  them.  In 
engineering  work  the  mortar  for  concrete  is  commonly 
formed  from  hydraulic  cement,  the  term  beton  being 
also  frequently  used  to  designate  hydraulic  concrete. 

In  preparing  concrete  by  hand  the  mortar  is  mixed 
in  the  usual  manner;  then  the  stone  is  spread  over  the 


232  HYDRAULIC  CEMENT. 

top  of  the  layer  of  mortar  and  thoroughly  mixed  with 
it  by  turning  with  shovels.  The  stone  should  be 
sprinkled  before  being  mixed  with  the  mortar,  suffi- 
ciently to  wet  its  surfaces  and  prevent  the  absorption 
of  the  water  from  the  mortar,  thus  promoting  the 
adherence  of  the  mortar  to  the  aggregate. 

Mortar  for  concrete  should  never,  as  is  frequently 
done,  be  reduced  to  a  fluid  state;  not  only  is  the 
resulting  strength  of  the  mortar  reduced  by  so  doing, 
but  it  cannot  be  properly  mixed  with  the  aggregate  to 
form  a  homogeneous  mass,  as  the  cement  washes  out 
of  the  mixture.  The  mortar  should,  however,  be  suf- 
ficiently soft  to  mix  readily  with  the  aggregate  to  a 
cohesive  mass,  which  may  be  placed  and  compacted 
without  difficulty  in  the  work.  The  consistency  of 
concrete  must  in  each  instance  depend  upon  its  nature 
and  method  of  use;  the  greatest  strength  may  usually 
be  attained  by  mixing  somewhat  dry  and  heavily 
ramming,  the  mortar  being  of  such  consistency  that 
the  concrete  becomes  somewhat  jelly-like,  water  being 
brought  to  the  surface  in  ramming.  An  extreme 
either  of  dryness  or  wetness  may  be  injurious. 

Mechanical  mixers  are  frequently  employed  for  pre- 
paring concrete,  and  are  very  useful  in  saving  labor 
where  considerable  quantities  are  used.  There  are  a 
number  of  forms  which  have  proven  effective  in  use, 
but  it  seems  unnecessary  to  enter  into  a  discussion  of 
them  here. 

The  aggregate  used  for  concrete  should  be  as  hard 
and  durable  as  possible,  and  that  of  angular  form  is 
preferable  to  rounded.  Angular  forms  give  a  greater 
surface  for  the  adherence  of  the  mortar  in  proportion 


CEMENT-MORTAR  AND   CONCRETE.  233 

to  volume  while  leaving  a  less  volume  of  interstices  to 
be  filled  with  mortar.  The  materials  should  be  uni- 
form in  quality.  Where  gravel  is  used  which  varies 
in  quality,  it  should  be  blended  by  mixing  in  order 
to  obtain  uniform  strength  in  the  concrete.  Porous 
aggregates  are  to  be  avoided,  as  they  are  likely  to 
absorb  the  cement-  When  the  materials  are  absorb- 
ent, they  should  be  saturated  in  sprinkling  before 
using,  in  order  to  avoid  withdrawing  water  from  the 
mortar  before  setting  takes  place. 

The  quantity  of  sand  used  in  concrete  should  be 
such  as  is  necessary  to  fill  the  voids  in  the  aggregate, 
while  the  quantity  of  cement  depends  upon  the 
strength  necessary  in  the  work  under  consideration. 
When  the  concrete  is  required  to  be  water-tight,  the 
amount  of  cement  paste  must  be  sufficient  to  fill  the 
interstices  in  the  mixture  of  stone  and  sand.  The 
quantity  of  sand  necessary  to  fill  the  interstices  in  the 
stone  may  be  determined  by  filling  a  measure  with 
stone  as  closely  as  possible,  and  then  measuring  the 
quantity  of  water  which  can  be  poured  into  the  meas- 
ure; this  gives  the  volume  of  sand  required.  If  the 
proper  quantity  of  damp  sand  be  added  to  the  stone  in 
the  measure  by  shaking  it  down  so  as  to  fill  the  voids, 
the  volume  of  water  which  can  then  be  put  in  the 
measure  is  the  volume  of  cement  paste  necessary  to 
fill  the  voids  in  the  aggregate. 

The  strength  of  concrete  usually  varies  nearly  in 
proportion  to  the  amount  of  cement  used  in  forming 
it.  When  a  strong  concrete  is  desired,  it  should  be 
obtained  by  increasing  the  richness  of  the  mortar  in 
cement,  not  by  increasing  the  proportion  of  mortar  to 


234  HYDRAULIC  CEMENT. 

large  material  above  the  point  at  which  the  sand  fills 
the  interstices  in  that  material.  If  the  proportion  of 
sand  be  less  than  this,  the  resulting  concrete  will  be 
porous  and  not  thoroughly  solidified ;  if  it  be  greater, 
the  excess  of  sand  may  be  an  element  of  weakness  in 
the  concrete. 

In  the  use  of  concrete  in  considerable  masses  the 
main  body  of  the  work  is  sometimes  formed  of  very 
weak  concrete,  with  a  facing  of  stronger  water-tight 
concrete  to  protect  it.  This  weak  concrete  is  fre- 
quently formed  by  omitting  the  sand  altogether  and 
simply  coating  the  stone  lightly  with  neat  cement, 
causing  the  stones  to  adhere  to  each  other,  thus  form- 
ing a  mass  sufficiently  firm  for  foundations  in  many 
locations  when  protected  by  a  covering  of  richer  con- 
crete. The  voids  in  a  mass  of  ordinary  broken  stone 
vary  from  about  4/10  to  5/io  of  the  volume,  depending 
upon  its  uniformity  in  size.  Where  there  is  consid- 
erable variation  in  size,  the  voids  may  be  somewhat 
less.  When  the  interstices  are  to  be  filled,  it  is  desir- 
able that  the  aggregate  contain  material  of  various 
sizes,  to  reduce  the  volume  of  interstices.  For  this 
reason  small  gravel  is  sometimes  mixed  with  broken 
stone  in  the  preparation  of  concrete. 

The  proportions  in  common  use  for  concrete  of 
Portland  cement  vary  from  I  part  cement,  2  parts 
sand,  and  5  parts  broken  stone  to  I  part  cement,  4 
parts  sand,  and  8  or  10  parts  broken  stone  or  gravel. 
Usually  the  mortar  is  made  richer  when  natural  cement 
is  used.  The  proportions,  of  course,  vary  with  the 
character  of  the  materials  to  be  used  as  well  as  that 
of  the  /ork  to  be  done,  and  can  only  be  properly 


CEMENT-MORTAR  AND  CONCRETE.  235 

determined  by  the  exercise  of  good  judgment,  in  the 
light  of  experience. 

ART.  75.     YIELD  OF  MORTAR  AND  CONCRETE. 

The  volume  of  mortar  formed  by  mixing  given 
quantities  of  cement  and  sand  depends  upon  the  den- 
sities of  the  materials  and  the  volume  of  interstices  in 
the  sand.  It  is  affected  also  by  the  method  of  pre- 
paring the  mortar,  the  uniformity  of  the  mixing,  and 
the  degree  of  compactness  given. 

The  net  volume  of  materials  entering  into  the  com- 
position of  mortar  or  concrete  is  readily  found  from 
their  weights  and  densities,  but  it  represents  only 
approximately  the  resulting  volume.  An  accurate 
knowledge  of  the  yield  of  any  particular  mixture  is  to 
be  obtained  only  by  experiment  upon  the  materials  to 
be  employed. 

Portland  cement  is  usually  sold  in  barrels  containing 
about  375  Ibs.  Natural  cements  are  lighter,  and  are 
put  up  in  barrels  of  260  to  320  Ibs.  Barrels  of  Rosen- 
dale  cements  usually  contain  300  Ibs. 

The  amount  of  neat  cement  paste  made  by  a  given 
weight  of  cement  powder  varies  with  the  specific 
gravity  of  the  cement  and  the  amount  of  water  neces- 
sary in  gauging.  The  lighter  cements  require  more 
water  and  yield  less  paste  for  a  given  volume  of 
cement  than  the  heavier  ones.  To  form  a  cubic  foot 
of  plastic  paste  requires  usually  from  75  to  90  Ibs.  of 
natural-cemerfit  powder;  about  80  to  85  Ibs.  of  Rosen- 
dale  cement  being  required,  while  about  95  to  loolbs. 
of  Portland  cement  are  necessary. 


236  HYDRAULIC  CEMENT. 

In  mixing  sand-mortar,  where  the  cement  and  sand 
are  proportioned  by  volume  measured  loose,  the 
quantities  required  to  form  a  cubic  yard  of  mortar  are 
approximately  as  follows: 

Uatural  Cement.      Portland  Cement.  Sand. 


Pounds. 

Pounds. 

Cu.  Yd. 

to  i  mortar. 

.  .  .  1050  to  1250 

1350  to  1530 

.65  to  .70 

to  2 

.  .  .  640  to  720 

810  to  920 

.80  to  .85 

to  3   " 

...  500  to  575 

620  to  690 

•  93  to  .96 

to  4   " 

—  400  to  460 

500  to  575 

I.OO 

to  5   " 

...  32010  375 

400  to  460 

I.OO 

For  concrete,  when  the  aggregate  is  broken  stone 
of  uniform  size,  it  is  necessary,  in  order  to  fill  the  in- 
terstices with  mortar,  that  the  volume  of  mortar  be  50$ 
to  60%  that  of  the  aggregate.  For  such  concrete  a 
mixture  of  about  .9  cubic  yard  of  broken  stone  with 
.50  to  .55  cubic  yard  of  the  mortar  as  given  above 
yields  about  one  cubic  yard  of  concrete.  This  gives 
the  proportions  sometimes  employed  for  strong  con- 
crete: I  part  cement,  2  parts  sand,  and  4  parts  broken 
stone;  or  I  part  cement,  3  parts  sand,  and  5  parts 
broken  stone. 

Where  the  stone  is  more  irregular  in  size,  or  if 
gravel  of  smaller  size  be  added,  a  smaller  proportion 
of  mortar  may  give  good  results.  Thus,  .9  cubic  yard 
of  broken  stone  with  .4  cubic  yard  of  gravel  and  .3 
cubic  yard  of  mortar  has  been  found  to  yield  i  cubic 
yard  of  good  concrete.  This,  using  I  to  2  mortar, 
gives  the  proportion  I  part  cement,  2  parts  sand,  3 
parts  gravel,  and  7  parts  broken  stone. 

When  the  amount  of  mortar  used  is  less  than  that 
indicated  above,  and  the  interstices  in  the  aggregate 


CEMENT-MORTAR   AND   CONCRETE.  237 

are  not  filled,  the  yield  of  concrete  is  about  equal  to 
the  volume  of  aggregate  employed. 

ART.  76.     MIXTURES  OF  LIME  AND  CEMENT. 

Slaked  lime  is  sometimes  mixed  with  hydraulic 
cement  for  the  purpose  of  decreasing  the  cost  of  con- 
struction. Experiments  seem  to  indicate  that  a  very 
considerable  percentage  of  lime  may  frequently  be 
added  without  material  loss  of  strength  in  the  mortar. 

With  Portland  cement  the  addition  of  lime  weakens 
the  mortar  somewhat,  the  decrease  in  strength  aug- 
menting rapidly  as  the  proportion  of  lime  increases. 

With  some  American  natural  cements  it  has  been 
found  that  a  certain  amount  (sometimes  30$  to  40^)  of 
lime  may  be  added  without  sensibly  decreasing  the 
strength  of  the  mortar  or  impairing  its  hydraulic  prop- 
erties. This  may  be  due  to  puzzolanic  action  on  the 
part  of  the  cement,  which  is  of  high  hydraulic  index. 

When  mortar  is  not  to  be  used  under  water,  and 
only  moderate  strength  is  necessary,  it  may  often  be 
economical  to  form  the  mortar  by  the  admixture  of 
lime,  better  results  being  obtained  than  by  using  a 
higher  proportion  of  sand.  The  mortar  thus  formed 
is  less  porous  than  that  made  with  a  larger  proportion 
of  sand,  and  it  is  also  more  plastic  and  easier  to  work. 
In  making  the  mixture  the  lime  is  ordinarily  slaked  in 
the  usual  manner  and  used  in  the  form  of  paste, 
although  it  may  be  slaked  to  powder  and  mixed  dry 
with  the  cement.  By  the  first  method  the  thorough 
slaking  of  the  lime  is  insured. 

The  admixture  of  lime  causes  the  cement  to  become 


238  HYDRAULIC  CEMENT. 

slower-setting,  the  quick-setting  cement  being  affected 
more  strongly  than  the  less  active  ones. 

In  France  a  small  proportion  of  Portland  cement  is 
sometimes  added  to  hydraulic  lime  for  the  purpose  of 
accelerating  the  setting  and  increasing  the  strength  of 
the  lime. 

Mixtures  of  natural  and  Portland  cement  have  fre- 
quently been  used  in  the  United  States  for  the  pur- 
pose of  modifying  the  action  of  the  quick-setting 
material  or  of  cheapening  construction.  They  seem 
generally  to  give  results  compounded  of  those  which 
would  be  obtained  by  using  them  singly. 

The  results  of  all  these  mixtures  will  be  found  to 
vary  with  the  particular  cement  employed,  and  the 
effect  can  only  be  known  by  trial  in  each  instance.  In 
all  cases,  to  get  good  results,  the  mixtures  must  be 
very  intimate. 

ART.  77.     THE  FREEZING  OF  MORTAR. 

Mortar  of  good  Portland,  or  of  many  kinds  of  nat- 
ural cement,  is  not  injured  by  freezing,  when  frozen 
before  it  is  set.  The  cement  sets  with  extreme  slow- 
ness, if  at  all,  while  frozen,  but  after  thawing  it  sets 
and  hardens  properly.  Mortar  frozen  for  short 
periods — a  few  days — does  not  set  while  frozen,  but 
the  experiments  of  Mr.  Cecil  B.  Smith  at  McGill  Uni- 
versity seem  to  show  that  if  kept  frozen  for  a  sufficient 
period  it  may  finally  set  while  frozen. 

The  hardening  of  cement  which  has  been  frozen  is 
much  more  slow  than  that  unfrozen,  but  it  may  ulti- 
mately gain  the  same  strength. 


CEMENT-MORTAR  AND  CONCRETE.  239 

Masonry  constructed  during  freezing  weather  is  fre- 
quently injured  by  freezing,  notwithstanding  the  fact 
that  the  cement  itself  shows  no  loss  of  strength  due  to 
freezing.  The  effect  of  frost  coming  upon  the  work 
before  it  is  fully  hardened  is  frequently  to  distort  or 
cause  unequal  settlement  in  it,  and  sometimes  repeated 
freezing  and  thawing  gradually  causes  the  mortar  to 
be  thrown  out  of  place  or  perhaps  to  become  cracked 
and  disintegrated  on  the  outside.  The  construction 
of  cement  masonry  during  freezing  weather  is  there- 
fore usually  more  or  less  hazardous,  unless  some 
means  be  adopted  of  preventing  the  freezing  action. 
Many  instances  may,  however,  be  cited  where  ex- 
treme cold  has  not  injured  work  constructed,  without 
such  precaution,  with  Portland-cement  mortar,  and  it 
is  claimed  by  many  engineers  that  Portland  may  be 
used  with  impunity  in  freezing  weather,  but  usually 
it  is  not  placed  in  work  while  a  freezing  temperature 
prevails.  It  is  commonly  agreed  that  most  natural 
cements  should  not  be  used  when  a  very  low  tempera- 
ture is  likely  to  reach  the  work  in  advance  of  it  having 
attained  good  strength,  and  instances  are  numerous  of 
work  having  been  injured  by  changing  temperature  of 
winter  weather,  although  it  may  not  have  frozen  for 
considerable  time  after  setting. 

Salt  is  quite  commonly  used  in  cold  weather  to 
prevent  the  freezing  of  mortar  while  it  is  soft.  A 
strong  solution,  frequently  a  saturated  one,  is  em- 
ployed. The  salt,  by  preventing  the  freezing  of  the 
water,  prevents  any  distorting  or  disrupting  action 
upon  the  work  due  to  the  change  in  volume  of  the 
mortar.  The  use  of  salt  considerably  decreases  the 


240  HYDRAULIC   CEMENT. 

activity  of  the  cement,  and  mortar  may  stand  in  a  soft 
condition  at  freezing  temperatures  and  finally  set  when 
the  temperature  becomes  sufficient  to  induce  action. 

The  loss  in  early  strength  of  cement-mortar  which 
has  been  mixed  with  salt  water  on  exposure  to  low 
temperature  before  setting  is  usually  greater  than  that 
of  mortar  without  the  salt  and  exposed  at  the  same 
temperature. 

The  effect  of  salt  upon  the  strength  of  various  kinds 
of  cement  is  quite  different.  In  nearly  all,  the  strength 
of  mortar  kept  in  air  is  increased  by  its  use.  When 
the  mortar  is  kept  under  water,  most  cements  have 
an  access  of  early  strength  from  the  use  of  salt,  which 
is  lost  later,  the  final  strength  being  somewhat  reduced. 
This  is  true  of  most  Portland  cements.  Some  natural 
cements  suffer  a  material  loss  of  strength  when  mixed 
with  salt  water,  while  others  are  entirely  ruined  by  a 
low  temperature  with  or  without  the  use  of  salt.  Care 
should  always  be  taken  to  determine  the  action  of  salt 
and  cold  upon  the  particular  cement  before  using  it  in 
this  manner. 

It  is  advisable  in  using  salt  to  protect  the  mortar 
from  contact  with  water  immediately  after  setting,  as 
sometimes  salt  mortar  which  has  been  exposed  to  low 
temperature  may  lose  its  cohesion  if  submerged  soon 
after  setting. 

Soda  has  sometimes  been  employed  to  prevent  the 
freezing  of  mortar,  but  its  use  has  not  become  exten- 
sive, and  has  usually  proven  unsatisfactory. 

Hot  water  should  not  be  used  in  mixing  mortar  in 
freezing  weather.  It  not  only  decreases  the  strength 
of  the  mortar,  but  renders  it  more  liable  to  injury  from 


CEMENT-MORTAR  AND  CONCRETE.       24! 

frost.  Heating  the  stones  or  bricks  in  the  construc- 
tion of  masonry  in  freezing  weather  may  be  beneficial, 
as  serving  to  accelerate  the  setting  and  keep  the  mor- 
tar from  freezing  while  soft. 

The  injury  done  to  mortar  by  low  temperatures  is 
probably  not  usually  due  to  freezing  before  setting, 
but  to  alternate  thawing  and  freezing  while  work  is 
still  fresh,  before  hardening  is  sufficiently  advanced  to 
render  the  mortar  capable  of  adequately  resisting  the 
expansive  forces.  The  effect  of  frost  upon  mortar 
which  has  set  is  similar  to  that  upon  stone  or  brick, 
and  is  due  to  the  increase  in  volume  of  water  freezing 
in  its  pores.  Its  effect  therefore  depends  both  upon 
the  porosity  of  the  mortar  and  upon  the  strength  it 
possesses  to  resist  disruption.  The  more  rapid  acqui- 
sition of  strength  by  Portland  cements  may  give  them 
the  advantage  they  possess  in  this  regard. 

Prof.  Le  Chatelier,  from  his  experiments  upon  the 
matter,  concludes  as  follows:  "  This  disintegration, 
like  that  of  frozen  stone,  is  more  easily  accomplished 
when  the  mortar  offers  small  mechanical  resistance, 
when  the  total  volume  of  voids  is  large,  and  when  the 
dimensions  of  each  separate  void  are  small.  When  the 
voids  are  sufficiently  large,  the  ice  breaks  with  a  pres- 
sure less  than  that  which  will  rupture  the  mortar. 
For  this  reason  mortars  of  large  sand  are  less  affected, 
the  voids  being  larger  and  less  numerous." 

ART.  78.     POROSITY  AND  PERMEABILITY  OF 
MORTAR. 

The  porosity  of  cement-mortar  depends  rather  upon 
the  manipulation  of  the  materials  in  gauging  than 


242  HYDRAULIC  CEMENT. 

upon  the  quality  of  the  cement.  When  the  quantity 
of  cement  is  insufficient  to  fill  the  voids  in  the  sand, 
spaces  are  left  which  permit  the  absorption  of  water 
without  increasing  the  volume  of  the  mortar. 

In  gauging  mortar  air-bubbles  attach  themselves  to 
the  wet  sand,  the  number  of  which  is  greater  as  the 
mortar  is  mixed  more  wet.  Working  the  mortar  tends 
to  eliminate  them.  Voids  in  the  mortar  are  also 
caused  by  the  evaporation  of  surplus  water  used  in 
mixing.  Porosity  is  greater  as  the  quantity  of  water 
used  in  gauging  is  increased  and  as  the  sand  used  is 
finer. 

The  permeability  of  cement-mortars  varies  with  the 
quality  of  the  cement  and  the  circumstances  of  its  use. 
Mortar  of  neat  Portland  cement  may  be  made  prac- 
tically impermeable  under  a  considerable  head  of 
water;  that  composed  of  cement  and  sand  seems 
always  more  or  less  permeable,  but  when  properly 
proportioned  and  mixed  eventually  permits  very  little 
water  to  pass. 

The  permeability  of  mortar  decreases  rapidly  with 
its  age:  for  the  first  few  days  or  weeks  after  mixing, 
water  passes  quite  freely  through  it,  but  as  the  har- 
dening process  approaches  completion  its  power  of 
resistance  is  in  this  particular  greatly  augmented. 

If  blocks  of  mortar  be  submitted  to  the  continuous 
filtration  of  water,  the  permeability  diminishes  very 
rapidly,  and  after  a  few  months  all  mortars,  except 
those  of  very  coarse  sand  and  feeble  proportion  of 
cement,  become  practically  impermeable. 

Both  the  porosity  and  permeability  are  less  for 
mortar  rich  in  cement  than  for  that  in  which  the  pro- 


CEMENT-MORTAR  AND   CONCRETE.  243 

portion  of  cement  is  small.  Mortar  mixed  dry  is 
penetrated  more  readily  than  that  mixed  to  a  plastic 
or  semi-wet  condition.  With  the  lapse  of  time,  how- 
ever, the  mortar  mixed  dry,  if  constantly  exposed  to 
water,  approaches  the  others  in  resistance  to  permea- 
tion. The  thoroughness  of  mixing  and  degree  of 
compacting  employed  are  more  important  factors  than 
the  absolute  quantity  of  water  used  in  mixing 

Fine  sand,  according  to  the  experiments  of  M.  Alex- 
andre,  renders  the  mortar  more  porous  and  less  per- 
meable than  coarse  sand.  When  the  sand  is  of 
varying  sizes  both  the  porosity  and  permeability  may 
be  low.  In  any  case,  to  attain  a  reasonable  resistance 
to  penetration,  it  is  necessary  that  the  interstices  in 
the  sand  be  entirely  filled  with  cement.  Cleanliness 
of  the  sand,  its  freedom  from  all  foreign  material,  is  of 
first  importance  in  the  preparation  of  impermeable 
mortar. 

Masonry  of  ordinary  brick  or  stone  can  only  be 
made  impervious  by  the  application  of  a  coating  of 
some  kind  to  its  face.  A  plastering  of  neat  cement 
or  rich  mortar  may  sometimes  be  used  for  this  purpose, 
and  coatings  of  asphalt  or  coal-tar  have  sometimes 
been  successfully  employed. 

In  concrete  work  where  imperviousness  is  essential, 
it  may  be  advisable,  as  with  masonry,  to  coat  the  face 
of  the  concrete.  In  order  that  concrete  may  be 
reasonably  water-tight,  it  is  necessary  that  the  quantity 
of  cement-mortar  used  in  preparing  it  be  sufficient  to 
fill  the  voids  in  the  large  material  employed,  as  well 
as  that  the  voids  in  the  sand  be  completely  filled  with 
cement  paste  in  making  the  mortar. 


HYDRAULIC   CEMENT. 


ART.  79.     EXPANSION  AND  CONTRACTION  OF 
MORTAR. 

In  the  use  of  large  masses  of  masonry  or  concrete 
the  change  that  is  liable  to  occur  in  the  volume  of 
mortar  may  frequently  become  of  importance,  and  it 
may  be  necessary  to  make  provision  by  which  changes 
in  dimension  an  take  place  without  in:ury  to  the 
work. 

The  coefficient  of  expansion  for  neat  cement  under 
the  action  of  heat  is,  as  previously  stated,  about  the 
same  as  for  iron,  although  it  may  vary  in  individual 
instances.  For  mortars  containing  sand,  the  coefficient 
is  less  than  for  neat  cement. 

Cements  differ  considerably  in  their  behavior  during 
the  continuance  of  the  hardening  process,  as  to  the 
change  that  takes  place  in  the  volume  of  the  mortar. 
Unsound  cement  is  apt  to  swell  and  become  distorted 
at  the  commencement  of  the  process  of  disintegration, 
and  of  course  any  considerable  change  of  this  nature 
indicates  the  probable  destruction  of  the  mortar. 
Perfectly  sound  cement,  although  not  altered  in  form, 
is  usually  changed  somewhat  in  dimensions  during 
hardening:  if  the  mortar  be  conserved  in  dry  air,  a 
slight  shrinkage  takes  place ;  if  under  water,  the  mor- 
tar swells  a  little. 

Prof.  Swain,  in  a  series  of  experiments  at  the 
Massachusetts  Institute  of  Technology  for  a  committee 
of  the  American  Society  of  Civil  Engineers,  found 
that  for  small  blocks  of  mortar  the  change  was  the 
same  in  all  directions;  that  for  neat  cements  the 


CEMENT-MORTAR  AND  CONCRETE.  245 

linear  contraction  in  air  varied  from  0. 14$  to  0.32$  for 
the  first  twelve  weeks  after  mixing,  and  the  linear  ex- 
pansion in  water  varied  from  0.04$  to  0.25$.  When 
sand  was  used  the  change  was  less,  giving  a  contrac- 
tion in  air  from  o.o8#  to  0.17$,  and  an  expansion  in 
water  of  from  0.00$  to  0.08$. 

The  rapidity  of  the  change  varies  somewhat  with 
the  activity  of  the  cement;  the  conclusion  being  that 
a  quick-setting  cement  changes  more  in  volume  than  a 
slow-setting  one. 

Further  experiment  is  desirable,  that  the  action  of 
the  various  classes  of  cement  may  be  better  under- 
stood. 

ART.  80.     EFFECT  OF  RETEMPERING  MORTAR. 

Masons  frequently  mix  water  in  considerable  quan- 
tities, and,  if  the  mass  becomes  stiffened  before  being 
used  by  the  setting  of  the  cement,  add  more  water 
and  work  again  to  a  soft  or  plastic  condition.  After 
the  second  tempering  the  cement  is  much  less  active 
than  at  first,  and  remains  a  longer  time  in  a  workable 
condition. 

This  practice  is  not  usually  approved  by  engineers, 
and  is  not  permitted  in  good  engineering  construction, 
although  there  is  some  dispute  as  to  its  injurious 
effect.  M.  Alexandre,  from  an  extensive  series  of 
experiments,*  concludes  that  no  injury  is  usually  done 
to  mortar  by  retempering,  provided  sufficient  water  be 
added  to  make  the  mortar  plastic  at  the  second  work- 

*  Annales  des  Ponts  et  Chaussdes,  1888,  vol.  i.  p.  375. 


246  HYDRAULIC   CEMENT. 

ing.  The  hardening  of  mortar  so  treated  is  very  slow 
at  first,  but  it  may  subsequently  (the  tests  extend  over 
three  years)  gain  as  much  strength  as  when  gauged 
immediately  upon  mixing. 

It  is  also  frequently  claimed  that  the  adhesive  prop- 
erties of  mortar  are  improved  by  giving  it  the  "  second 
set."  The  common  practice  of  masons  who  set  fire- 
place tiling  and  similar  work  is  based  upon  this  idea. 
Further  experiment  to  determine  this  point  would  be 
interesting. 

The  results  of  experiments  other  than  those 
already  quoted  have  seemed  to  show  that  in  some 
instances  injury  is  done  to  mortar  by  retempering, 
some  cements  even  refusing  to  set  the  second  time. 
Until  more  is  known  of  the  action  of  the  material 
when  subjected  to  this  treatment,  it  seems  advisable 
to  mix  only  such  quantity  at  once  as  may  be  used 
before  the  initial  set  of  the  cement,  and  to  reject 
any  material  that  may  have  set  before  being  placed 
in  the  work. 


APPENDIX. 


SPECIFICATIONS  FOR  THE  RECEPTION  OF 
CEMENT. 

IN  the  discussion  which  has  been  given  of  the 
various  tests  applied  to  cement,  the  requirements  of 
specifications  have  been  considered,  but  it  is  thought 
desirable  to  append  a  few  actual  specifications  to  show 
the  requirements  employed  in  practice. 

Some  engineers  who  use  considerable  quantities  of 
cement  of  a  few  brands,  or  of  a  single  brand,  employ 
no  specifications,  but  depend  upon  the  reliability  of 
the  brand,  or  perhaps  upon  occasional  examinations 
to  show  that  the  material  is  up  to  standard.  This  is 
frequently  the  practice  upon  ordinary  railroad  work, 
and  in  some  instances,  ivhere  the  use  is  continuous 
and  private  contracts  may  be  made  for  the  material, 
is  quite  satisfactory. 

Some  specifications  (quite  frequently  employed) 
make  no  mention  of  any  specific  requirements,  but 
call  for  cement  which  shall  be  satisfactory  to  the  en- 
gineer in  charge  of  the  work,  and  lodge  in  him  full 
power  to  accept  or  reject  the  material.  The  effect  of 
such  a  specification  depends  upon  the  circumstances 


248  APPENDIX. 

under  which  it  is  employed.  When  used  as  a  speci- 
fication for  work,  in  open  competition,  it  is  very  apt 
to  prove  unsatisfactory;  but  when  it  represents  the 
established  practice  of  an  office  dealing  with  particular 
brands  of  cement,  it  may  not  be  objectionable. 

There  seems,  generally,  to  be  no  good  reason  for 
stating  specifications  in  an  indefinite  manner.  The 
conditions  to  be  imposed  may  as  easily  be  plainly 
stated,  and  thus  leave  no  doubt  as  to  the  requirements. 
In  some  instances,  however,  engineers  consider  a 
specification  of  this  kind  advantageous  where  the 
cement  to  be  used  is  limited  to  a  few  accepted  brands 
(particularly  with  natural  cements),  the  tests  to  be  im- 
posed varying  with  the  brand  and  being  only  for  the 
purpose  of  showing  that  the  various  lots  of  cement  are 
normal  in  action.  In  such  a  case  the  tests  to  be  im- 
posed are  usually  an  understood,  though  not  an  ex- 
pressed, part  of  the  specifications. 

The  specifications  which  follow,  A,  B,  C,  D,  E,  are 
thought  to  represent  fairly  well  the  range  of  require- 
ments in  the  best  American  practice 

Specifications  "A"  represent  about  the  common 
requirements  for  ordinary  masonry,  but  are  more 
complete  and  explicit  in  statement  than  is  common. 
The  tensile  test  requirements  vary  considerably  in 
various  specifications,  being  frequently  much  higher 
where  permanent  laboratories  are  maintained,  as  in 
specifications  "  D  "  and  "  E." 

Specifications  "  B  "  have  much  the  same  require- 
ments, but  apply  the  Faija  warm-water  test  for  sound- 
ness. 

Specifications  "  C  "  are  intended  for  cement  to  be 


SPECIFICATIONS  FOR  THE  RECEPTION  OF  CEMENT.    249 

used  for  heavy  work  in  sea-water.  Soundness  is 
assured  by  applying  the  hot  test,  combined  with  a  limit 
of  sulphuric  acid  and  magnesia.  The  requirements 
are  high,  but  may  be  met  without  difficulty  by  most 
of  the  leading  brands  of  Portland  cement,  and  are  con- 
sidered necessary  because  of  the  importance  of  the 
work  and  its  exposure  to  the  action  of  sea-water. 

It  is  quite  common  to  place  considerable  reliance 
upon  the  brand  in  selecting  cement,  and  in  many 
specifications  the  approval  of  the  brand  is  an  essential 
condition.  This,  seemingly,  places  an  arbitrary  power 
in  the  hands  of  the  engineer,  but  may  often  increase 
the  likelihood  of  getting  good  material,  while  perhaps 
saving  the  trouble  and  loss  of  time  incident  to  testing 
material  obviously  unfit  for  use. 

A, 

PENNSYLVANIA    RAILROAD    COMPANY. 
P.,  W.  &  B.  R.  R.       N.  C.  Ry.       W.  J.  &  S.  R.  R. 

STANDARD   SPECIFICATIONS   FOR  CEMENT. 

Cement  will  be  tested  by  the  Railroad  Company, 
upon  its  receipt,  in  accordance  with  the  following 
specifications,  and  such  tests  are  to  be  final  as  deter- 
mining the  matter  of  its  acceptance  or  rejection. 

The  cement  for  testing  shall  be  selected  by  taking, 
from  each  of  six  well-distributed  barrels  in  each  car- 
load received,  sufficient  cement  to  make  five  to  ten 
briquettes;  these  six  portions,  after  being  thrown 
together  and  thoroughly  mixed,  will  be  assumed  to 
represent  the  average  of  the  whole  car-load. 


250  APPENDIX; 

Fineness.  —  Not  more  than  io#  of  any  cement 
shall  fail  to  pass  through  a  No.  50  sieve  (2500  meshes 
per  square  inch),  wire  to  be  No.  35,  Stubb's  wire- 
gauge. 

Cracking. — Neat  cement,  mixed  to  the  consistency 
of  stiff  plastic  mortar,  and  made  in  the  shape  of  flat 
cakes,  two  or  three  inches  in  diameter  and  one-half 
inch  thick,  with  thin  edges,  when  hard  enough  shall 
be  immersed  in  water  for  at  least  two  days.  If  they 
crack  along  the  edges  or  become  contorted,  the 
cement  is  unfit  for  use. 

Tensile  Strength. — The  test  for  tensile  strength 
shall  be  made  with  briquettes  of  standard  form,  as 
recommended  by  the  American  Society  of  Civil  En- 
gineers, moulds  for  which  will  be  furnished  from  the 
office  of  the  Engineer  Maintenance  of  Way.  They 
must  have  an  average  tensile  strength  not  less  than 
that  given  in  the  table  below: 


One 
Day. 

One 

Week. 

Four 
Weeks. 

American  Natural  Cement: 
Neat                   

7O 

qc 

50 

•}O 

60 

American  and  Foreign  Portland  Cement: 
Neat                            .  .         

Proportion  of  Water. — The  proportion  of  water 
used  in  making  briquettes  varies  with  the  fineness, 
age,  and  other  conditions  of  the  cement  and  the  tem- 
perature of  the  air,  but  is  approximately  as  follows: 


SPECIFICATION^  FOR  THE  RECEPTION  OF  CEMENT.    2$ I 

Neat  Cement.— Portland,   2(5#— to    30$.     Natural, 
20#  to  30$. 

I  part  cement,  I  part  sand,  about  15$  total  weight 
of  cement  and  sand. 

i  part  cement,  2  parts  sand,  about  12$  total  weight 
of  cement  and  sand. 

Mixing. — The  cement  and  sand,  in  proper  propor- 
tions, shall  be  mixed  dry,  and  all  the  water  specified 
added  at  one  time,  the  mixing  to  be  as  rapid  as  possi- 
ble to  secure  a  thorough  mixture  of  the  materials,  and 
the  mortar,  when  stiff  and  plastic,  to  be  firmly  pressed 
to  make  it  solid  in  the  moulds  without  ramming,  and 
struck  off  level. 

Moulding. — The  moulds  to  rest  directly  on  glass, 
slate,  or  other  non-absorbent  material.  As  soon  as 
hard  enough,  briquettes  are  to  be  taken  from  moulds 
and  kept  covered  with  a  damp  cloth  until  immersed. 

In  the  one-day  test  briquettes  shall  remain  on  the 
slab  for  one  hour  after  being  removed  from  mould  and 
twenty-three  hours  in  water.  In  one  week  or  more 
test,  briquettes  shall  remain  in  air  one  day  after  being 
removed  from  moulds  and  balance  of  time  in  water. 

Briquettes  are  to  be  broken  immediately  after  being 
taken  from  the  water.  Stress  to  be  applied  at  a  uni- 
form rate  of  four  hundred  pounds  per  minute,  starting 
each  time  at  zero. 

No  record  to  be  taken  of  briquettes  breaking  at 
other  than  fti^'sjiiallest  section. 

Sand. — The  sand  used  in  test  shall  be  clean,  sharp, 
and  dry,  and  be  such  as  shall  pass  a  No.  20  sieve  (400 
meshes  per  square  inch),  wire  to  be  No.  28,  Stubb's 
wire-gauge,  and  to  be  caught  in  a  No.  30  sieve  (900 


252  APPENDIX. 

meshes  per  square  inch),  wire  to  be  No.  31,  Stubb's 
wire-gauge. 

Water. — Ordinary  fresh,  clean  water,  having  a  tem- 
perature between  60°  and  70°  Fahr.,  shall  be  used  for 
the  mixture  and  immersion  of  all  samples. 

Proportions. — The  proportions  of  cement  and  sand 
and  water  shall  in  all  cases  be  carefully  determined  by 
weight. 

In  preparing  briquettes  for  test,  sufficient  material 
is  to  be  taken  to  make  one  briquette  at  a  time,  and 
enough  of  water  being  added  to  make  a  stiff  plastic 
paste  as  above  stated. 

The  temperature  of  the  testing-room  not  to  be 
below  45°  Fahr. 

By  order  of  the  General  Manager. 

JOSEPH  T.  RICHARDS, 

Engineer  Maintenance  of  Way, 

OFFICE  OF  THE  ENGINEER  OF  MAINTENANCE  OF  WAY 
PHILADELPHIA,  January  10,  1897. 

B. 

SPECIFICATIONS  OF  THE    CANADIAN   PACIFIC 
RAILWAY  COMPANY. 

Mr.  P.  ALEX.  PETERSON,  Chief  Engineer. 
(Extract  from  General  Specifications  for  Rubble  Masonry.) 
"  5.  The  cement  used  in  making  concrete  or  mor- 
tar   shall    be    freshly    ground     Portland     cement    of 
approved  brand,  or  such  other  cement  as  the  Engineer 
may  approve.      It  shall  weigh  not  less  than  1 10  Ibs. 
to  the  struck  bushel;  and  not  less  than  90$  of  it  shall 
pass  through  a  sieve  containing  2500  meshes  per  square 


SPECIFICATIONS  FOR  THE  RECEPTION  OF  CEMENT.    2$3 

inch.  The  tensile  strength  of  the  neat  cement  after 
being  kept  in  water  at  a  temperature  of  about  60° 
Fahr.  for  seven  days  shall  not  be  less  than  350  Ibs. 
to  the  square  inch.  Also,  when  mixed  with  one  part 
of  cement  to  three  parts  of  sand  by  measure,  it  shall 
stand  170  Ibs.  to  the  square  inch  at  the  end  of  28 
days. 

"  In  preparing  sand  for  this  test,  sand  shall  be  re- 
jected which  passes  through  a  sieve  made  of  No.  31 
wire  with  900  meshes  to  the  square  inch,  or  which 
will  not  pass  through  a  sieve  made  of  No.  28  wire  with 
400  meshes  to  the  inch. 

"  A  pat  made  and  submitted  to  moist  heat  and 
warm  water  at  a  temperature  of  about  100°  Fahr. 
shall  show  no  sign  of  blowing  in  24  hours. 

"  Cement  shall  be  tested  by  the  Engineer  on  deliv- 
ery ;  and  it  shall  be  kept  in  a  dry  place,  and  in  as  good 
order  as  when  delivered,  until  it  is  used." 


C. 

EXTRACTS  FROM  SPECIFICATIONS  FOR  FURNISH- 
ING PORTLAND  CEMENT  FOR  WALLABOUT 
IMPROVEMENT,  BROOKLYN,  N.  Y. 

W.  E.  BELKNAP,  Engineer. 

11  9.  All  the  cement  to  be  furnished  under  this  con- 
tract must  be  of  the  class  of  such  material  known  as 
high-grade  '  Portland  '  cement  free  from  lumps,  dry 
and  finely  ground,  and  unless  as  otherwise  specified, 
must  be  of  one  or  more  of  the  following  brands, 
known  as  '  DyckerhofT, '  '  Alsen's  White  Label,'  and 
'  Stettiner  Star  Brand.'  Cement  of  other  brands 


2$4  APPENDIX. 

may  be  furnished,  provided  the  Contractor  submits 
proof  satisfactory  to  the  Engineer  that  it  has  been  used 
in  making  large  masses  of  concrete,  which  have  been 
exposed  to  the  action  of  sea-water  for  at  least  two 
years  previous  to  the  date  of  this  contract,  and  that 
such  concrete  now  shows  no  signs  of  deterioration 
which  might  be  imputed  to  defective  qualities  in  the 
cement. 

"  10.  All  the  cement  shall  be  composed  of  lime, 
silica,  and  alumina  in  their  proper  forms  and  propor- 
tions, be  as  free  as  possible  from  all  other  substances, 
and  contain  no  adulterant  in  injurious  proportions. 
The  ratio  of  the  weight  of  silica  and  alumina  to  the 
weight  of  the  lime  in  the  cement  shall  not  be  less  than 
45/100.  The  cement  shall  not  contain  more  than  3/ 
of  magnesia  nor  more  than  i#  of  sulphuric  acid. 

"  ii.  The  cement  shall  not  have  a  lower  specific 
gravity  than  3.10. 

"  12.  All  the  cement  shall  be  of  a  fineness  so  that 
99^  by  weight  shall  pass  through  a  No.  50  sieve  (2500 
meshes  per  square  inch)  of  No.  35  wire;  90$  shall  pass 
through  a  No.  100  sieve  (10,000  meshes  per  square 
inch)  of  No.  40  wire,  and  70%  shall  pass  through  a 
No.  200  sieve  (40,000  meshes  per  square  inch)  of  No. 
45  wire.  All  wire  numbered  as  per  '  Stubb's  '  gauge. 

"13.  The  cement  must  not  take  its  '  initial '  set  in 
less  than  30  minutes  after  mixing.  It  shall  take  its 
'  hard  '  set  in  not  less  than  3  hours  and  in  not  more 
than  8  hours. 

"  The  cement  will  be  said  to  have  attained  its 
'  initial  '  and  its  '  hard  '  set  when  it  bears  without 
indentation  respectively  a  wire  of  1/12  inch  diameter 


SPECIFICATIONS  FOR  THE  RECEPTION  OF  CEMENT. 


loaded  to  weigh  1/4  pound,  and  a  wire  of  1/24  inch 
diameter  loaded  to  weigh  I  pound,  it  having  been 
previously  mixed  neat  with  about  25$  of  its  weight  of 
water,  and  worked  for  from  one  to  three  minutes  into 
a  stiff  plastic  paste. 

"  14.  All  the  cement  shall  be  capable  of  developing 
a  tensile  strength  under  various  conditions  as  follows: 


Age. 

Tensile 

Strength 

in 

Pounds 

per 

Square 

Inch. 

Mixed  neat   with  about 
25$  01  water  by  weight 
and     worked     to     stiff 
plastic  paste. 

24  hours 
7  days, 
28     " 

,  in  water  after  hard  set 
I  in  air,  6  in  water,  70° 
I  "  "  27  " 

150 
400 
600 

Mixed  with  3  parts  sand 

by  weight,   and  about 

I2#of  combined  weight 

7  days, 

I  in  air,  6  in  water,  70° 

150 

of  sand  and  cement  of 

28     " 

T  "  "  27  " 

240 

water    to   stiff    plastic 

paste. 

'  To  determine  the  tensile  strength,  4  briquettes  of 
the  cement  under  each  of  the  above  conditions  will  be 
broken  in  a  '  Riehle  '  or  Fairbanks  or  other  testing- 
machine  satisfactory  to  the  engineer. 

"  The  sand  to  be  used  in  making  briquettes  will  be 
clean,  dry  crushed  quartz,  trap-rock  or  granite,  pass- 
ing a  No.  20  sieve  of  No.  28  wire,  and  caught  on  a 
No.  40  sieve  of  No.  31  wire  '  Stubb's  '  gauge.  The 
briquettes  will  be  of  the  form  recommended  by  the 
American  Society  of  Civil  Engineers. 

"15.  All  cement  must  be  sound  in  every  respect, 


256  APPENDIX. 

and  show  no  indications  of  distortion,  change  of 
volume,  or  blowing  when  subjected  in  the  form  of  pats 
to  exposure  in  air  and  fresh  and  sea  water  of  tempera- 
ture from  60°  to  212°,  as  follows: 

"  The  pats  will  be  made  of  neat,  unsifted  cement, 
mixed  with  fresh  water  to  the  same  consistency  as 
before  stated  for  briquettes,  and  will  be  about  3  inches 
in  diameter,  having  a  thickness  at  the  centre  of  about 
1/2  inch,  tapering  to  about  1/8  inch  at  the  edges. 
They  will  be  moulded  on  plates  of  glass  and  kept 
thereon  during  examination. 

"  (a)  One  or  more  of  these  pats  will,  when  set 
'  hard,'  be  placed  in  fresh  water  of  temperature 
between  60°  and  70°  for  from  I  to  28  days. 

"  (b)  One  or  more  of  these  pats  will  be  allowed  to 
set  in  moist  air  at  a  temperature  of  about  200°  for 
about  3  hours.  It  will  then  be  placed  and  kept  in 
boiling  water  for  a  period  of  from  6  to  24  hours. 

"  (c)  One  or  more  of  these  pats  will  be  allowed  t& 
set  in  moist  air  at  a  temperature  of  about  100°  for  3 
hours;  it  will  then  be  placed  and  kept  in  water  of 
temperature  of  110°  to  115°  for  a  period  of  from  24 
to  48  hours. 

"  (d~)  One  or  more  of  these  pats  may  be  subjected 
to  any  or  all  of  the  above  indicated  tests  ( (a),  (b),  and 
(c)  ),  using  sea-water  instead  of  fresh  water. 

"  (e)  One  pat  will  be  kept  in  the  air  for  28  days  and 
its  color  observed,  which  shall  be  uniform  throughout, 
of  a  bluish  gray,  and  free  from  yellow  blotches. 

"  A  failure  to  pass  test  (b)  will  not  necessarily 
cause  the  rejection  of  the  cement,  provided  it  passes 
the  other  tests  for  soundness  as  noted  in  (a),  (c),  (d), 


SPECIFICATIONS  FOR  THE  RECEPTION  OF  CEMENT.    257 

and  (<?),  and  is  satisfactory  in  other  respects  to  the 
engineers. 

"  16.  All  the  above  tests  may  be  modified  and 
other  tests,  in  addition  thereto  or  in  substitution 
therefor,  be  required,  at  the  discretion  of  the  engineer, 
to  practically  determine  the  fitness  of  the  cement  for 
its  intended  use. 

"  17.  It  is  agreed  by  the  party  of  the  second  part 
that  he  will  pay  all  the  costs  of  testing  the  cement  to 
determine  its  composition,  quality,  and  character  to 
the  satisfaction  of  the  engineer. 

11  1 8.  It  is  further  agreed  that  the  tests  shall  be 
made  in  the  manner  as  indicated  on  the  schedule  on 
file  in  the  office  of  the  Engineer,  and  that  they  shall 
be  made  by  the  Engineer  or  by  one  or  more  of  the 
following  parties:  R.  W.  Hildreth  &  Co. ;  Riehle  Bros. 
Testing-machine  Co.;  E.  &  T.  Fairbanks  &  Co.,  of 
New  York  City;  and  Booth,  Garrett  &  Blair,  of  Phila- 
delphia, Pa. 

"  19.  It  is  agreed  that  as  many  tests  shall  be  made 
to  determine  the  composition  and  specific  gravity  of 
the  cement  as  indicated  in  Articles  9  and  10,  as  shall 
be  desired  by  the  Engineer.  It  is  agreed  that  one 
sample  shall  be  tested  for  each  100  barrels  or  more  to 
determine  the  quality  of  the  cement,  as  per  Articles 
u,  12,  13,  and  14. 

"  20.  All  the  cement  must  be  furnished  in  the 
'  original  package  '  in  strong  substantial  barrels,  which 
shall  be  plainly  marked  with  the  brand  or  mark  of  the 
maker  of  the  cement. 

"21.  Each  barrel  must  be  properly  lined  with 
paper  or  other  material  so  as  to  effectually  protect  the 


2$8  APPENDIX. 

cement  from  dampness.  Any  cement  damaged  by 
water  to  such  an  extent  that  the  damage  can  be  ascer- 
tained from  the  outside  will  be  rejected  in  toto,  and 
the  barrels  unopened.  Barrels  containing  a  large 
proportion  of  lumps  will  also  be  rejected.  Broken 
barrels  of  cement,  if  otherwise  satisfactory,  will  be 
counted  as  half-barrels." 

"25.  It  is  agreed  that  the  quality  and  character  of 
any  lot  of  cement  shall  be  determined  by  the  Engineer 
by  the  tests  as  above  called  for,  and  as  per  provisions  of 
Article  30  hereof,  said  tests  to  be  made  upon  such  pro- 
portions of  the  whole  amount  of  cement  in  any  lot  as 
he  may  deem  proper,  and  it  is  further  agreed  that  his 
decision  as  to  the  acceptance  or  rejection  of  the  cement 
under  this  contract  shall  be  final  and  conclusive." 

"  30.  It  is  further  agreed  that  the  Commissioner 
may  reject  and  refuse  to  accept  any  cement  which  in 
his  opinion  is  unfit  for  the  work  for  which  it  is  intended 
without  making  tests  of  the  same  and  without  giving 
any  reasons  »or  such  opinion  to  the  Contractor,  but  all 
cement  must  before  acceptance  pass  satisfactorily,  to 
the  Engineer,  all  the  tests  herein  prescribed." 

(With  reference  to  Article  30,  Mr.  Belknap  says: 
"  I  might  explain,  in  view  of  its  seemingly  giving  an 
arbitrary  power  to  the  Commissioner,  that  it  was  in- 
serted in  order  that  we  might  avoid  the  trouble  and 
delay  of  testing  any  brands  which  on  the  face  of  it 
appeared  to  us  to  be  entirely  unfit  for  the  work.") 


SPECIFICATIONS  FOR  THE  RECEPTION  OF  CEMENT.     259 


D. 

SPECIFICATIONS    FOR    MUNICIPAL    WORK    IN    ST. 
LOUIS,  MO. 

Mr.  M.  L.  HOLMAN,   Water  Commissioner. 

(Extract  from  "Specifications  for  Foundation  of  Stand-pipe  No.  3, 
St.  Louis  Water  Works.") 

"  26.  All  cement  for  the  work  herein  specified  shall 
be  of  the  best  quality  of  American  Portland.  Cement 
without  the  manufacturer's  brand'  will  be  rejected 
without  test. 

"  27.  All  cement  furnished  will  be  subject  to  in- 
spection and  rigorous  tests,  of  such  character  as  the 
Water  Commissioner  shall  determine,  and  any  cement 
which,  in  the  opinion  of  the  Water  Commissioner,  is 
unsuitable  for  the  work  herein  specified  will  be  re- 
jected. 

"  28.  If  a  sample  of  the  cement  shows  by  chemical 
analysis  more  than  2%  of  magnesia  (MgO),  or  more 
than  2%  anhydrous  sulphuric  acid  (SO3),  the  shipment 
will  be  rejected. 

"  29.  To  secure  uniformity  in  cement  of  approved 
brands,  all  cement  received  on  the  work  shall  be  sub- 
ject to  tests  for  checking  or  cracking,  and  to  the  fol- 
lowing tests  for  fineness  and  tensile  strength. 

"  30.  All  cement  shall  be  fine-ground,  and  85$ 
shall  readily  pass  a  sieve  having  10,000  meshes  to  the 
square  inch. 

"31.  All  cement  shall  be  capable  of  withstanding 
a  tensile  stress  of  400  Ibs.  per  square  inch  of  section, 


26o  APPENDIX. 

when  mixed  neat,  made  into  briquettes,  and  exposed 
24  hours  in  air  and  6  days  under  water. 

"32.  All  cement  shall  be  put  up  in  well-made 
barrels,  and  all  short-weight  or  damaged  barrels  will 
be  rejected.  Samples  for  testing  shall  be  furnished  at 
such  times  and  in  such  manner  as  may  be  required. 
On  all  barrels  of  rejected  cement  inspection  marks 
will  be  placed,  and  the  Contractor  shall  in  no  case 
allow  these  barrels  to  be  used. 

"  33.  In  measuring  cement  for  mortar  or  concrete, 
the  standard  volume  of  a  barrel  of  cement  shall  be 
determined  by  comparing  its  net  weight  with  the 
weight  of  one  cubic  foot  of  thoroughly  compacted 
neat  cement. 

"  34.  All  cement  for  use  on  the  works  shall  be  kept 
under  cover,  thoroughly  protected  from  moisture, 
raised  from  the  ground,  by  blocking  or  otherwise,  and 
dry  until  used.  The  Contractor  shall  keep  in  storage 
a  quantity  of  accepted  cement  sufficient  to  secure  the 
uninterrupted  progress  of  the  work. 

"35.  Accepted  cement  may  be  re-inspected  at  any 
time,  and  if  found  to  be  damaged  or  of  improper 
quality  will  be  rejected.  All  rejected  cement  shall  be 
at  once  removed  from  the  work." 

(Mr.  Holman  states  that  in  his  future  specifications 
he  intends  to  reduce  the  allowable  sulphuric  acid  to 


SPECIFICATIONS  FOR  THE  RECEPTION  OF  CEMENT.    261 


E. 


SPECIFICATIONS   FOR   MUNICIPAL  WORK   IN 
PHILADELPHIA. 


GEORGE  s.  WEBSTER,  DEPARTMENT  OF  PUBLIC  WORKS, 

RICHARD  L.(HHUMFPHNRGEYEER'  BUREAU    OF    SURVEYS. 

INSPECTOR  OF  CEMENTS. 


SPECIFICATIONS   FOR   CEMENT  AND   MORTAR. 


1.  Inspection. — All    cements   shall   be   inspected, 
and  those  rejected  shall  be  immediately  removed  by 
the    Contractor.      The  Contractor    must   submit  the 
cement,    and  afford  every  facility   for  inspection  and 
testing,  at  least  twelve  (12)  days  before  desiring  to  use 
it.     The  Inspector  of  Cements  shall  be    notified  at 
once  upon  the  receipt  of  each  shipment  of  cement  on 
the  work. 

2.  Packages. — No    cement   will    be    inspected    or 
allowed  to  be  used  unless  delivered  in  suitable  pack- 
ages, properly  branded. 

3.  Storage. — On  all  main  sewers,  bridges  (unless 
otherwise  ordered),  and  such  branch  sewers  or  other 
work  as  the  Chief   Engineer  may  designate,  shall  be 
provided  a  suitable  house  for  storing  the  cement. 

4.  Protection. — Accepte'd  cement,  if  not  used  im- 
mediately,  must   be  thoroughly   protected    from   the 
weather,    and   never  placed   on   the   ground   without 
proper  blockings. 


262  APPENDIX. 

5.  Failure. — The  failure  of  a  shipment  of  cement 
on  any  work  to  meet  these  requirements  may  prohibit 
further  use  of  the  same  brand  on  that  work. 

The  acceptance  of  a  cement  to  be  used  shall  rest 
with  the  Chief  Engineer,  and  will  be  based  on  the  fol- 
lowing requirements: 

NATURAL  CEMENT. 

1.  Specific  Gravity  and  Fineness — Natural  cem- 
ent   shall  have  a   specific    gravity   of    not    less    than 
2.7,  and  shall  leave,  by  weight,  a  residue  of  not  more 
than  two  (2)  per  cent  on  a  No.  50  sieve,  fifteen  (15)  per 
cent  on  a  No.  100  sieve,  and  thirty-five  (35)  per  cent 
on  a  No.   200  sieve;    the  sieves  being  of  brass-wire 
cloth  having  approximately  2400,  10,200,  and  35,700 
meshes  per  square   inch,    the   diameter   of   the   wire 
being  .0090,  .0045,  and  .0020  of  an  inch  respectively. 

2.  Constancy  of  Volume. — Pats   of    neat  cement 
one-half  (£)  inch  thick  with  thin  edges,  immersed  in 
water   after    "hard"    set,    shall    show    no    signs    of 
"  checking"  or  disintegration. 

3.  Time  of  Setting. — It  shall  develop  "  initial  " 
set  in  not  less  than  ten  (10)  minutes,  or  "  hard  "  set  in 
less  than  thirty  (30)  minutes.      This  being  determined 
by  means  of  the  Vicat  needle  from   pastes  of  neat 
cement  of  normal  consistency,  the  temperature  being 
between  60°  and  70°  Fahr. 

4.  Tensile   Strength. — Briquettes  one  (i)  square 
inch  in  cross-section  shall  develop  the  following  ulti- 
mate tensile  strengths: 


SPECIFICATIONS  FOR   I  HE  RECEPTION  OF  CEMENT.    263 

Age.  Strength. 

24  hours  (in  water  after  "  hard  "  set) 100  Ibs. 

•   7  days  (i  day  in  air,  6  days  in  water) 200  Ibs. 

28  days  (i  day  in  air,  27  days  in  water) 300  Ibs. 

7  days  (i  day  in  air,  6  days  in  water),  i  part  of 

cement  to  2  parts  of  Standard  quartz  sand. .   125  Ibs. 
28  days  (i  day  in  air,  27  days  in  water),  i  part  of 

cement  to  2  parts  of  Standard  quartz  sand. .   200  Ibs. 

PORTLAND  CEMENT. 

5.  Specific  Gravity  and  Fineness. — Portland  cem- 
ent shall  have  a  specific  gravity  of  not  less  than  3, 
and  shall  leave,  by  weight,  a  residue  of  not  more  than 
one  (i)  per  cent  on  a  No.  50  sieve,  ten  (10)  per  cent 
on  a  No.  100  sieve,  and  thirty  (30)  per  cent  on  a  No. 
200  sieve;    the  sieves  being  the  same  as   previously 
described. 

6.  Constancy  of  Volume — Pats   of   neat  cement 
one-half  (£)  inch  thick,  with  thin  edges,  immersed  in 
water   after   "  hard  "    set,    shall    show    no    signs    of 
"  checking  "  or  disintegration. 

7.  Time   of  Setting.  —  It    shall    require   at    least 
thirty  (30)  minutes  to  develop  "  initial  "  set,   under 
the  same  conditions  as  specified  for  natural  cement. 

Tensile  Strength. — Briquettes  of  cement  one  (i) 
inch  square  in  cross-section  shall  develop  the  follow- 
ing ultimate  tensile  strengths: 

Age.  Strength. 

24  hours  (in  water  after  "  hard  "  set) 175  Ibs 

7  days  (i  day  in  air,  6  days  in  water) 500  Ibs. 

28  days  (i  day  in  air,  27  days  in  water) 600  Ibs. 

7  days  (i  day  in  air,  6  days  in  water),  i  part  of 

cement  to  3  parts  of  Standard  quartz  sand. .  170  Ibs. 
28  days  (i  day  in  air,  27  days  in  water),  i  part  of 

cement  to  3  parts  of  Standard  quartz  sand. .  240  Ibs. 


264  APPENDIX. 

9.  Additional  Requirements. — All  cements  shall 
meet  such  additional  requirements  as  to  "  hot  water," 
"  set,"  and  "  chemical  "  tests  as  the  Chief  Engineer 
may  determine.  The  requirements  for  "  set  "  may  be 
modified  where  the  conditions  are  such  as  to  make 
it  advisable. 


1.  Sand  and  Water. — Sand  shall   be    sharp,   sili- 
cious,    dry-screened,    tide-washed    bar    sand,    or    ap- 
proved  flint    bank    sand,    free    from    loam    or    other 
extraneous  matter.     The  water  must  be  fresh,  and  free 
from  dirt.     When  so  directed  by  the  Chief  Engineer, 
salt  water  may  be  required,    to   prevent  the  mortar 
from     freezing,    when     absolutely    necessary    to     lay 
masonry  in  cold  weather. 

2.  Composition. — Portland-cement  mortar  shall  be 
composed  of  one  part  of  cement  and  three  parts  of 
sand.      Natural-cement  mortar  shall  be  composed  of 
one  part  of  cement  and  two  parts  of  sand. 

Mortar  for  pointing,  grouting,  bedding  coping- 
stones  and  bridge-seats^shall  be  composed  of  one  part 
Portland  cement  and  two  parts  sand.  A  greater  por- 
tion of  cement  shall  be  used  when  required. 

3.  Mixing.  —  The    ingredients,    properly    propor- 
tioned by  measurement,    must  be  thoroughly  mixed 
dry  in  a  tight  box  of   suitable   dimensions,  and  the 
proper  amount  of  clean  water  added  afterwards.     No 
greater  quantity  is  to  be  prepared  than  is  required  for 
immediate  use,  and  any  that  has  "  set  "  shall  not  be 
retempered  or  used  in  any  way. 


SPECIFICATIONS  FOR  THE  RECEPTION  OF  CEMl-.NT.    265 

4.  Tensile  Strength. — Mortar  taken  from  the 
mixing  box,  and  moulded  into  briquettes  one  square 
inch  in  cross-section,  shall  develop  the  following 
ultimate  tensile  strengths: 

Age.  Strength. 

7  days  (i  day  in  air,  6  days  in  water),  i  part  of 

natural  cement  to  2  parts  of  sand 50  Ibs. 

28  days  (i  day  in  air,  27  days  in  water),  i  part  of 

natural  cement  to  2  parts  of  sand 125  Ibs. 

7  days  (i  day  in  air,  6  days  in  water),  i  part  of 

Portland  cement  to  3  parts  of  sand 125  Ibs. 

28  days  (i  day  in  air,  27  days  in  water),  i  part  of 

Portland  cement  to  3  parts  of  sand 175  Ibs. 

PHILADELPHIA,  January  9,  1897. 


PROPERTY  or 
C.   W.  BOYNTON, 
VOL.  Ho. 


This  book  is  DUE  on  the  last  date  stamped  below 


tf  16  1335 
JAN    3  iyJo 
OEC  13  1939 


UC  SOUTHERN  REGIONAL  LIBRARY  FACILITY 


